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| Acre |
Acre:This article is about the unit of measure known as the acre. For other definitions, see Acre (disambiguation).
An acre is an English unit of area. It is most frequently used to describe areas of land.
The UK has a definition of the acre in [http://www.opsi.gov.uk/si/si1995/Uksi_19951804_en_2.htm The Units of Measurement Regulations 1995] as 4,046.856422 4 m². This is equivalent to 43,560 square feet using the definition of foot in the same source.
The US has a definition of the acre in [http://ts.nist.gov/ts/htdocs/230/235/appxc/appxc.htm NIST Handbook 44] as 43,560 square feet. However, the US has two definitions of foot (international foot and survey foot) and thus two definitions of acre:
- The international acre is 4,046.856422 4 m². This is based on international foot of 0.3048 m.
- The US survey acre is 4,046.87261 m². This is based on the US survey foot of 1200/3937 m.
Related linear measurements
Two obsolete, but related, measurements are the acre's length and the acre's breadth.
- 1 acre's length = 1 furlong, 40 poles, or 220 yards
- 1 acre's breadth = 1 chain, 4 poles, or 22 yards
An international acre is equivalent to exactly:
- 4 046.856 422 4 m² (SI unit)
- 40.468 564 224 a,
- 0.404 685 642 24 ha,
- 43 560 square feet,
- 4840 square yards,
- 160 square rods,
- 4 rood,
- 1/640 square mile,
- a 10:1 rectangle of 1 furlong by 1 chain.
- 10 square chains.
An acre is equivalent to approximately:
- a square of side 208.71 feet (63.61 metres).
One square mile is 640 acres. A square parcel of land ¼ mile wide is 40 acres. A square parcel of land ½ mile on a side is 160 acres, the usual land tract under the Homestead Act in the United States. This results in common field lengths of ½ mile, with every rod in width equal to one acre.
An American Football field covers approximately 1.32 acres.
History
The acre was selected as approximately the amount of land tillable by one man behind an ox in one day. This explains its rectangular definition one-chain by one-furlong parcel of land; a long narrow strip of land is more efficient to plough than a square plot, since the plough does not have to be turned so often. Statutory values were enacted in England by acts of
- Edward I,
- Edward III,
- Henry VIII,
- George IV and
- Victoria - the British "Weights and Measures Act" of 1878 defined it as containing 4840 square yards.
See also
- Conversion of units
- Acre-foot
- Acre (Scots)
External links
- [http://www.opsi.gov.uk/si/si1995/Uksi_19951804_en_2.htm The Units of Measurement Regulations 1995]
- [http://ts.nist.gov/ts/htdocs/230/235/appxc/appxc.htm NIST Handbook 44]
Category:Units of area
Category:Imperial units
Category:Customary units in the United States
Category:Real estate
ja:エーカー
Acre (disambiguation)
Acre may refer to:
- An acre, a unit of land area measurement.
- The city of Acre is the English name for the ancient city called Akko in Hebrew and Akka in Arabic, in modern Israel.
- The state of Acre in Amazonia, Brazil, named for the Crusader outpost.
- Acre, Lancashire
Imperial unitThis article is about post-1824 Imperial units, please see also English unit, U.S. customary unit or Avoirdupois.
----
The Imperial units or the Imperial system is a collection of English units, first defined in the Weights and Measures Act of 1824, later refined (until 1959) and reduced. The units were introduced in the United Kingdom and its colonies, including Commonwealth countries, but excluding the then already independent United States.
Relation to other systems
The distinction between this imperial system and the U.S. customary units (also called standard units there) or older British/English units/systems and newer additions is often not drawn precisely. Most length units are shared among the Imperial and U.S. systems, albeit partially and temporally defined slightly differently. Capacity measures differ the most due to the introduction of the Imperial gallon and the unification of wet and dry measures. The avoirdupois system only applies to weights; it has a long flavour and a short flavour for the hundredweight and ton.
The term imperial should not be applied to English units that were outlawed in Weights and Measures Act of 1824 or earlier, or which had fallen out of use by that time, nor to post-imperial inventions such as the slug or poundal.
Although most of the units are defined in more than one system, some subsidiary units were used to a much greater extent, or for different purposes, in one area rather than the other.
Measures of length
poundal.]]
After the 1 July 1959 deadline, agreed upon in 1958, the U.S. and the British yard were defined identically (0.9144 m) to the international yard. Metric equivalents in this article usually assume this latest official definition. Before this date, the most precise measurement of the Imperial Standard Yard was 0.914398416 m (Sears et al. 1928. Phil Trans A 227:281).
- The pole is also called rod or perch.
Until the adoption of the international definition of 1852 metres in 1970, the British nautical mile was defined as 6080 feet (1.85318 km). It was not readily expressible in terms of any of the intermediate units, because it was derived from the circumference of the Earth (like the original metre). Depth of water at sea was expressed in fathoms (6 feet = 1.8288 m).
Measures of area
Measures of volume
In 1824, Britain adopted a close approximation to the ale gallon known as the Imperial gallon. The Imperial gallon was based on the volume of 10 lb of distilled water weighed in air with brass weights with the barometer standing at 30 in and at a temperature of 62 °F. In 1963, this definition was refined as the space occupied by 10 lb of distilled water of density 0.998 859 g/mL weighed in air of density 0.001 217 g/mL against weights of density 8.136 g/mL. This works out to exactly 4.545 964 591 L, or 277.420 in³. The Weights and Measures Act of 1985 finally switched to a gallon of exactly 4.546 09 L (approximately 277.419 43 cu in) [http://www.sizes.com/units/gallon_imperial.htm].
The full table of British apothecaries' measure is as follows:
For a comparison to the U.S. customary system see the article on Comparison of the Imperial and US customary systems.
Measures of weight and mass
Britain has made some use of three different weight systems, troy weight, used for precious metals, avoirdupois weight, used for most other purposes, and apothecaries' weight, now virtually unused since the metric system is used for all scientific purposes.
The use of the troy pound (373.241 721 6 g) was abolished in Britain on January 6, 1879, with only the troy ounce (31.103 476 8 g) and its decimal subdivisions retained. In all the systems, the fundamental unit is the pound, and all other units are defined as fractions or multiples of it.
Note that the British ton is 2240 pounds (the long ton), which is very close to a metric tonne, whereas the ton generally used in the United States is the "short ton" of 2000 pounds (907.184 74 kg), both are 20 hundredweights. For more on Commonwealth-U.S. differences see Comparison of the Imperial and US customary systems.
Current use of Imperial units
British law now defines each Imperial unit entirely in terms of the metric equivalent. See the
[http://www.hmso.gov.uk/si/si1995/Uksi_19951804_en_2.htm Units of Measurement Regulations 1995]. This regulation effectively outlaws their usage in retail and trading except in previously established exceptions. This has now been proved by in court against the so called 'Metric Martyrs', a small group of market traders. Despite this, many small market traders still use the customary measures, citing customer preference especially among the older population.
In the United States and in a few Caribbean countries, the U.S. customary units, which are similar to Imperial units based upon older English units and in part share definitions, are still in common use. English units have been replaced elsewhere by the SI (metric) system. Most Commonwealth countries have switched entirely to the international system of units.
The United Kingdom completed its legal transition to SI units in 1995, but a few such units are still in official use: draught beer must still be sold in pints, most roadsign distances are still in yards and miles, and speed limits are in miles per hour, therefore interfaces in cars must have miles, and even though the troy pound was outlawed in Great Britain in the Weights and Measures Act of 1878, the troy ounce still may be used for the weight of precious stones and metals. The use of SI units is increasingly mandated by law for the retail sale of food and other commodities, but many British people still use Imperial units in colloquial discussion of distance (miles and yards), speed (miles per hour), weight (stones and pounds), liquid (pints and gallons) and height (feet and inches).
In Canada, the government's efforts to implement the metric system were more extensive: pretty much any agency, institution, or thing provided by the government will use SI units exclusively. Imperial units were eliminated from all road signs, although both systems of measurement will still be found on privately-owned signs (such as the height warnings at the entrance of a multi-storey parking facility). Temperatures in degrees Fahrenheit will occasionally be heard on English Canadian commercial radio stations, but only those that cater to older listeners. The law requires that measured products (such as fuel and meat) be priced in metric units, although there is leniency in regards to fruits and vegetables. Traditional units persist in ordinary conversation and may be experiencing a resurgence due to the reduction in trade barriers with the United States. Few Canadians would use SI units to describe their weight and height, although driver's licences use SI units. In livestock auction markets, cattle are sold in dollars per hundredweight (short, of course), whereas hogs are sold in dollars per hundred kilograms. Land is surveyed and registered in metric units, but imperial units still dominate in construction, house renovation and gardening talk (although "two-by-fours" don't actually measure 2×4", for example).
See also
- Conversion of units
- Cooking weights and measures
- Metrication
- Metrified English unit
- Unit of measurement
- Systems of measurement
- History of measurement
References
- Appendices B and C of [http://ts.nist.gov/ts/htdocs/230/235/h442003.htm NIST Handbook 44]
- Barry N. Taylor's [http://physics.nist.gov/Pubs/SP811/ NIST Special Publication 811], also available as [http://physics.nist.gov/Document/sp811.pdf a PDF file]
External links
- [http://www.metric.org.uk/ The UK Metric Association]
- [http://www.bwmaonline.com/ British Weights And Measures Association]
- [http://www.metric4us.com Metric4us.com]
- [http://laws.justice.gc.ca/en/w-6/109089.html Canada - Weights and Measures Act 1970-71-72]
- [http://193.120.124.98/gen531996a.html Ireland - Metrology Act 1996]
- [http://www.hmso.gov.uk/si/si1995/Uksi_19951804_en_2.htm UK - Units of Measurement Regulations 1995]
- [http://calc.skyrocket.de/en/ Online Unit Converter - Conversion of many different units]
- Jacques J. Proot's [http://users.aol.com/jackproot/met/spvolas.html Anglo-Saxon weights & measures] page.
-
Category:Systems of units
ja:ヤード・ポンド法
US customary unitsThe U.S. customary units, commonly known in the United States as English units or standard units, are the non-SI (non-metric) units of measurement that are currently used in the U.S., in some cases alongside the International System of Units. This system of units is similar to, but not to be confused with, the Imperial system which was used in the United Kingdom until 1995. Both systems derive from the evolution of local units over the centuries as a result of standardization efforts in England; the local units themselves mostly trace back to Roman and Anglo-Saxon units. Today, U.S. customary units are defined in terms of SI units.
The official policy of the United States government is to designate the metric system of measurement as the preferred system of weights and measures for U.S. trade and commerce. This process is known as metrication, and is evident in labeling requirements on food products, for example. However, for various reasons, customary units are still widely used on consumer products and in industrial manufacturing; only in specific scientific contexts are SI units generally preferred. Since everyday weights and measures are mostly non-SI, children in U.S. public schools are generally taught customary units before SI, although many schools are now attempting to teach SI units at an earlier age.
In most Commonwealth countries, such as Australia and New Zealand, where metrication has been more forcefully imposed and has encountered less resistance from industry and consumer market forces, metrication is relatively complete, although some informal usage of non-SI units remains, particularly in Canada. Although increasingly metric, the UK has taken some time to change over, and retains use of non-SI units, particularly in informal situations. In more populated and developed countries amongst the former British colonies, such as India, existing local weights and measures had been redefined based upon English units. Some of these are still in limited use, however the metric units are more or less the norm.
Other countries have had customary units of their own, sometimes very similar in root (Germanic, Roman), name and value to the ones listed below—foot or pound, for instance—but frequently, similar terms designate quite different sizes. For example, miles ranged from 1 to 10 kilometers. The standardization of these units was of varying quality, but was often comparable to or better than the U.S. customary system of the 19th century. Most were later redefined in terms of kilogram and meter. Often, unlike English units, they were rounded to "nice" SI values, leading to their use in colloquial speech, alongside SI terms, into the present day.
Historically, a wide range of non-SI units have been used in the United States. and United Kingdom, and in England before that, but many of these have fallen into disuse. This article only deals with the units commonly used or officially defined in the United States.
Units of length
The system for measuring length in the United States' customary system is based on the inch, foot, yard, and mile. However, for each of these units there exist two slightly different definitions, yielding two different systems of measure - international measure, and U.S. survey measure. The relationships between the different units within each measure is the same, but each measure has a slightly different definition in terms of metric units.
One inch international measure is exactly 25.4 millimeters, while one inch U.S. survey measure is defined so that 39.37 inches is exactly 1 meter. For most applications, the difference is insignificant (about 3 millimeter per mile). International measure is used for everyday use, engineering, and commerce in the United States, while survey measure is used only for surveying.
International measure, agreed in 1959, uses the same definition of the units involved as is used in the UK and other Commonwealth countries. Before that date, those other countries still used separate standards. U.S. survey measure uses an older definition of the units (specified by the former National Bureau of Standards in 1893) which the United States used prior to adopting international measure. Previous to this agreement, the US standard was identical to survey measure.
- 1 inch (in) = 25.4 mm
- 1 foot (ft) = 12 in = 30.48 cm
- 1 yard (yd) = 3 ft = 91.44 cm
- 1 mile (mi) = 5280 ft = 1760 yd = 1.609344 km
- 1 rod (unit) (rd) (also called pole or perch) = 16.5 ft = 5.0292 m
- 1 furlong (fur) = 40 rd = 660 ft = 201.168 m
- 1 mile (survey) = 8 fur = 5280 ft ≈ 1.609347 km
Sometimes, for surveying purposes, units known as Gunther's Chain Measure (or equivalently Surveyor's Chain Measure) are used. These units are defined by survey feet as follows:
- 1 link (li) = 7.92 in = 0.66 ft = 0.001 fur (approx. 201.168 mm)
- 1 chain (ch) (Gunter's) = 100 li = 66 ft (approx. 20.1168 m)
To measure depths at sea, fathoms are used:
- 1 fathom = 6 feet = 1.8288 m
- 1 cable length = 120 fathoms = 720 feet = 219.456 m (US Navy definition, there are others)
Units of area
The units of area in the U.S. customary system are mostly based on the units of length squared, e.g., square inch (sq in, 645.16 mm²). Since the U.S. customary system has two differing definitions of the foot (international and survey), there are also two differing definitions for the square foot.
- 1 square foot (sq ft) = 144 sq in = 929.0304 cm²
- 1 square rod (sq rd) = 272.25 sq ft = 25.29285264 m²
- 1 acre = 10 sq ch = 1 fur × 1 ch = 160 sq rd = 43,560 sq ft = 4046.8564224 m²
- 1 square mile (sq mi) = 27,878,400 sq ft = 3,097,600 sq yd = 640 acres = 2.589988110336 km²
The Public Land Survey System, used to divide land in most of the United States, uses the survey mile to divide land into regular square parcels, such "sections" and "townships." However, these terms aren't used for general area measurement, instead used to indicate particular parcels of land in a rectangular grid.
Units of capacity and volume
The cubic inch, cubic foot and cubic yard are commonly used for measuring volume. In addition, there is one group of units for measuring volumes of liquids, and one for measuring volumes of dry material.
Other than the cubic foot, cubic inch and cubic yard, these units are differently sized from the units in the Imperial system, although the names of the units are similar. Also, while the U.S. has separate systems for measuring the volumes of liquids and dry material, the Imperial system has one set of units for both.
Technically speaking, since these units are defined in terms of the inch, it would make a difference whether international or survey measure was used. However, in practice, the difference between the two definitions would be imperceptible, and in any case in defining volumes international measure is used.
Volume in general
- 1 cubic inch (in³ or cu in) = 16.387064 mL (or cm³)
- 1 cubic foot (ft³ or cu ft) = 1728 cu in ≈ 28.317 L
- 1 cubic yard (yd³ or cu yd) = 27 cu ft ≈ 7.646 hL
- 1 acre-foot = 43,560 cu ft ≈ 325,851 gallons ≈ 12,334.818 m³
Liquid volume
- 1 minim (min) = 1/480 fl oz ≈ 61.612 µL
- 1 fluid dram (fl dr) = 1/8 fl oz = 60 min ≈ 3.697 mL
- 1 fluid ounce (fl oz) = 1/128 gal = 8 fl dr ≈ 29.574 mL
- 1 gill (gi) = 7.21875 cu in = 4 fl oz ≈ 118.294 mL
- 1 cup = 2 gi = 8 fl oz ≈ 236.588 mL
- 1 pint (pt) = 2 cups = 4 gi = 16 fl oz ≈ 473.176 mL
- 1 fifth = 25.6 fl oz ≈ 757.082 mL
- 1 quart (qt) = 2 pt = 32 fl oz ≈ 946.353 mL
- 1 gallon (gal) = 231 cu in = 4 qt = 128 fl oz = 3.785411784 L
The gill—pronounced —is basically a paper unit which is never actually used in the United States.
Distilled liquor and wine were bottled in fifths until 1973; when the term "fifth" is used now it almost always means 750 mL.
Dry volume
- 1 pint (pt) ≈ 550.610 mL
- 1 quart (qt) = 2 pt ≈ 1.101 L
- 1 gallon (gal) = 4 qt = 268.8025 in³ = 4.404 842 803 2 L
- 1 peck (pk) = 8 qt = 2 gal ≈ 8.81 L
- 1 bushel (bu) = 2150.42 cu in = 4 pk ≈ 35.239 L
Units of mass
There have historically been four different English systems of mass: Tower weight, Troy weight, Avoirdupois system, and Apothecaries' system. Tower weight fell out of use (due to legal prohibition) centuries ago, and was never used in the United States. Troy weight is still used to weigh precious metals. Apothecaries weight, once used in pharmacy, has been largely replaced by metric measurements. Avoirdupois weight is the primary system of mass in the U.S. customary system.
The Avoirdupois units are legally defined as measures of mass, but the names of these units are sometimes applied to measures of force. For instance, in most contexts, the pound avoirdupois is used as a unit of mass, but in the realm of physics, the term "pound" can represent "pound-force" (a unit of force properly abbreviated as "lbf").
Troy weight, avoirdupois weight, and apothecaries weight are all defined in terms of the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds), the relationship between the grain and these other units within each system varies. For example, in apothecaries and troy weight, the pound and ounce are the same, but are different from the pound and ounce in avoirdupois, in terms of their relationships to grains and to each other. The systems also have different units between the grain and ounce (apothecaries has scruple and dram, troy has pennyweight, and avoirdupois has just dram). The dram was once known as the drachm.
To alleviate confusion, it is typical when publishing non-avoirdupois weights to mention the name of the system along with the unit. Precious metals, for example, are often weighed in "troy ounces", because just "ounce" would be more likely to be assumed to mean an ounce avoirdupois.
The pound avoirdupois, which forms the basis of the U.S. customary system of mass, is defined as exactly 453.59237 grams. All the other units of mass are defined in terms of it.
For the pound and smaller units, the U.S. customary system and the British Imperial system are identical. However, they differ when dealing with units larger than the pound. The definition of the pound avoirdupois in the British Imperial system is identical to that in the U.S. customary system.
Avoirdupois weight
See Avoirdupois.
- 1 grain (gr) = 64.79891 mg
- 1 dram (dr) = 27 11/32 gr = 1/16 oz ≈ 1.772 g
- 1 ounce (oz) = 16 dr = 437.5 gr ≈ 28.35 g
- 1 pound (lb) = 16 oz = 7000 gr = 453.59237 g
- 1 hundredweight (cwt) = 100 lb = 45.359 kg
- 1 ton (t) = 20 cwt = 2000 lb = 907.18474 kg ≈ 0.907 t
The ton and hundredweight above are referred to as the short ton, and the short hundredweight, to distinguish them from the British Imperial ton and hundredweight, which are larger and hence are referred to as the long ton and long hundredweight. The long ton has limited use in the United States.
- 1 long hundredweight = 112 lb ≈ 50.802 kg
- 1 long ton = 20 long cwt = 2240 lb ≈ 1016.047 kg ≈ 1.016 t
Apothecaries' weight
See Apothecaries' system of mass.
The grain has the same definition as for avoirdupois weight.
- 1 scruple (s ap) = 20 gr ≈ 1.296 g
- 1 dram apothecaries (dr ap) = 3 s ap ≈ 3.888 g
- 1 ounce apothecaries (oz ap) = 1 oz t = 8 dr ap = 480 gr ≈ 31.103 g
- 1 pound apothecaries (lb ap) = 1 lb t = 12 oz ap = 5760 gr ≈ 373.242 g
The pound and ounce apothecaries are identical to the pound and ounce troy.
Troy weight
The grain has the same definition as for Avoirdupois weight.
- 1 pennyweight (dwt) = 24 gr ≈ 1.555 g
- 1 ounce troy (oz t) = 20 dwt = 480 gr ≈ 31.103 g
- 1 pound troy (lb t) = 12 oz t = 5760 gr ≈ 373.242 g
Cooking measures
The most common cooking weights and measures in the U.S. are as follows:
- 1 teaspoon = 1/3 tbsp = 1/6 fl oz ≈ 5 mL
- 1 tablespoon (tbsp) = 1/2 fl oz = 4 fl dr ≈ 15 mL
- 1 cup = 8 fl oz ≈ 240 mL
- 1 stick (of butter) = ¼ lb = 4 oz ≈ 115 g
See Cooking weights and measures for more details.
Grain measures
These are derived from the volume measures and there have been more for other crops.
- 1 bushel (maize) = 56 lb ≈ 25.401 kg
- 1 bushel (wheat) = 60 lb ≈ 27.216 kg
Units of temperature
Traditionally, degrees Fahrenheit are used in the United States to measure temperatures.
- Pure water freezes at 32 °F and boils at 212 °F at 1 atm.
- Water saturated with common salt freezes at -6.02 °F.
- Conversion formula:
Other units
- British thermal unit
- Horsepower
- Hand
- Calorie
- Degree Rankine
- Board-foot
- R-value
See also
- History of measurement
- Systems of measurement
- Units of measurement
- English unit
- Imperial unit
- Comparison of the Imperial and US customary systems
- Conversion of units
- Approximate conversion between English and SI units
- Metrified English unit
- Metrication
- Metric system
- SI
External links
- Source: [http://ts.nist.gov/ts/htdocs/230/235/h442002.htm Appendix C, NIST Handbook 44, 2002 edition].
- Judson, Lewis B., Weights and Measures Standards of the United States: A brief history, NBS Special Publication 447, orig. iss. October 1963, updated March 1976 ([http://ts.nist.gov/ts/htdocs/200/202/SP%20447.pdf 46 page PDF file]).
- Jacques J. Proot's [http://users.aol.com/jackproot/met/spvolas.html Anglo-Saxon weights & measures] page.
Category:Imperial units
Category:Systems of units
ja:ヤード・ポンド法
simple:US units of measurement
Furlong]
A furlong is a measure of distance within Imperial units and U.S. customary units. Although its definition has varied historically, in modern terms it equals 660 feet or 220 yards, and is therefore equal to 201.168 metres. There are ten chains in a furlong and eight furlongs in a mile. The name "furlong" derives from the Old English words furh (furrow) and lang (long). It originally referred to the length of the furrow in one acre of a ploughed open field (a medieval communal field which was divided into strips). The system of long furrows arose because turning a team of oxen pulling a heavy plough was difficult. This offset the drainage advantages of short furrows and meant furrows were made as long as possible. For this reason, it was once also called an acre's length.
Distances for thoroughbred horse races in the United Kingdom, Ireland and the United States are given alternately in miles and furlongs ([http://www.sportinglife.com/racing/goodwood/course/ example]), but the unit is otherwise no longer in common use — and even in that discipline its usage is confined mainly to denoting distances of less than one mile. Its official use was abolished in the United Kingdom under the Weights and Measures Act 1985, which also abolished from official use many other traditional units of measurement.
Coincidentally, 5 furlongs is 1005.84 metres (exactly) and is therefore approximately 1 kilometre.
Trivia
An absurd unit of speed often misquoted is the furlong per fortnight, which converts to:
- 0.0001663095 metre per second or roughly one centimetre per minute (in SI units)
- 0.0005456349 feet per second (in Imperial units)
Thus:
- a car travelling at 60 km/h (37 mph) is travelling at a speed of 100,214.7 furlongs per fortnight;
- a Boeing 737 cruising at 420 knots or 216.2 m/s (i.e. typical 0.8 Mach cruise) is travelling at 1,300,013.7 furlongs per fortnight;
- the speed of light in vacuum is approximately 1.803
- 1012 furlongs per fortnight;
- one furlong per fortnight is 0.166 millimetres per second, which would be barely noticeable to the naked eye.
The city of Chicago's numbering system allots a measure of 800 to each mile. Logically, streets were subsequently laid out 8 to the mile. This means that every block in a typical Chicago neighborhood (in either North/South or East/West direction but rarely both) is precisely one furlong.
Category:Units of length
Category:Imperial units
Category:Customary units in the United States
ja:ハロン (単位)
Chain (unit)The chain is an English unit of length. It is defined as 66 feet (20.1168 metres). It is also known as the surveyor's chain, Gunter's chain or land chain.
Conversions
1 chain is equivalent to:
- 66 feet (exactly)
- 22 yards (exactly)
- 4 rods (exactly)
- 4 poles (exactly)
- 4 perches (exactly)
- 100 links
- 10 chains = 1 furlong
- 80 chains = 1 mile
Since the width of an acre was defined as one chain (with a length of one furlong), it was also known as an acre's breadth.
acre]
History
The term chain derives from the device commonly used for measurement of land in the past — a chain of 100 links, the Gunter's chain being the most common. The links were about eight inches long, made of heavy gauge wire, with a loop at each end. The links were joined end to end to create the chain by three rings between the links. This enabled the chain to be folded up, link by link, until all 100 were in a bundle which could be held in the hand. At each end were brass handles and the full chain measurement was between the outside extremities of the brass handles with the chain at full stretch on flat ground. If the chain had been folded correctly, an experienced chainman (surveyor's assistant) could fling the bundle out and it would unfold neatly with no snags. Another chainman would grab the handle, flick the chain to get it straight and then be ready to take the measurement. Long distances would be measured in bays of one chain, the actual chain being dragged forward for each bay.
With so many links in the chain there were many wearing surfaces and chains commonly were longer than the designated length. Also some surveyors added an extra link, so that their surveys always included a greater physical area than the actual measurements indicated (the landowners weren't going to complain!). When retracing old surveys with modern equipment a surveyor will almost always find his measurements between monuments are longer than the originals.
The unit was once important in everyday life, being one of the fundamental units of Imperial system in the United Kingdom and its colonies, and was used to some extent in engineering and surveying in the U.S.
In Britain, it was commonly used in the railway industry (where the measure is still in widespread use). Mapping by the Ordinance Survey (Britain's national mapping organisation) began in the early 19th century using the chain as the basic unit of measurement. All map scales at that time were expressed as a relative fraction of a chain or a mile (e.g. a one inch to ten chain scale was equivalent to 1:7920 or eight inches to a mile).
The use of the chain was once very common in laying out townships and mapping the U.S. along the train routes in the 19th century. In the U.S. a federal law was passed in 1785 (the Public Land Survey Ordinance) that all official government surveys must be done with a Gunter's chain (also referred to as the "surveyor's chain").
American surveyors sometimes used a longer chain of 100 feet (30.48 m), known as the engineer's chain or Ramsden's chain. In Texas, the vara chain of 20 varas (55.556 ft) was used in surveying Spanish land grants.
In agriculture, measuring wheels with a circumference of 0.1 chain are still common and readily available in the United States and Canada, at least. For a rectangular tract, multiply the number of turns of one of these wheels for each side, then divide by 1000 to get the area in acres.
The chain also survives, in fact if not always in name, in two other specific contexts.
- It is the length of the pitch, between the wickets, in cricket.
- It lies at the origin of the definition of an acre as 4840 square yards. The original acre was an area of land suitable for ploughing in a defined time, and was therefore not square; it measured one chain by one furlong (10 square chains).
In the laying out of towns in Australia and New Zealand, most building lots in the past were a quarter of an acre, measuring one chain by two and a half chains, and other lots would be multiples or fractions of a chain. The city of Melbourne is a classic example: surveyor Robert Hoddle divided the city into 24 ten-chain blocks, which still serve as the basic grid of the city. The street frontages of many houses in these countries are one chain wide—roads were almost always one chain wide (20.117 m) in urban areas, sometimes one and a half or two chains (30.2 m or 40.2 m). Laneways would be half a chain (10.1 m). In rural areas the roads were wider, up to 10 chains (201 m) where a stock route was required.
External links
- [http://www.pballew.net/arithm16.html#gunter Math Words]
- [http://www.unc.edu/~rowlett/units/introd.html How Many? A Dictionary of Units of Measurement], Russ Rowlett
- [http://www.orbitals.com/self/survey/chain/chain.html How to make a Gunter's Chain]
Category:Units of length
Category:Imperial units
Category:Surveying
Category:Customary units in the United States
Conversion of unitsThis article lists conversion factors between a number of units of measurement.
Conversion techniques
The simplest way to convert from one unit to another is to carry through the units themselves in the mathematical operation. To illustrate this process, consider the following examples.
You would like to convert 6 feet into metres. Consulting the table below and finding that one foot is exactly 0.3048 metre, you can now perform the mathematical conversion:
6 ft × 0.3048 m/ft = 1.8288 m
Notice that the "foot" units canceled out, leaving only metres, the desired result. (Since 0.3048 metre per foot have infinite precision, the precision of the answer is determined by the precision of the 6 ft figure; if, for example, you are defining the fathom, expressing it with 5 significant figures is correct. But if the 6 ft figure is a measurement, the result needs to be rounded appropriately.)
Say your height is 183 centimetres, and you wish to convert this into inches:
183 cm / (2.54 cm/in) = 72.0 in
To check our answer, we convert this result back into feet:
72 in / (12 in/ft) = 6.0 feet
which confirms the earlier result.
Multiple units can be manipulated in the same fashion:
7 mi/s × 1.609344 km/mi × 3600 s/h = 40,000 km/h
Thus, Earth escape velocity is about 7 miles per second, or 40,000 kilometres per hour. Notice that since the calculation started with one significant figure (the 7), the answer also has one significant figure (the 4 in 40,000).
Deciding whether to multiply or divide is determined by looking at the units and deciding which ones you want to "get rid" of. In the conversion just above, if we had divided by 3600 s/h instead of multiplying, the result would have come out in kilometre-hours per square second, clearly an incorrect and meaningless result.
Rounding of results
An important thing to remember is that the process of making a conversion cannot give you any more precise results than what you started with. While many of the conversion factors given in the tables below are exact, and others while not exact contain many significant digits, all the numbers you get after performing calculations on a calculator or with pencil and paper are not meaningful.
After using these conversion factors, be sure to round off the results appropriately.
See also
- False precision
- Accuracy and precision
- Significant figures
Tables of conversion factors
Key:
≡ — definition
= — exactly equal to
≈ — approximately equal to
(digits) — indicates the digits repeat infinitely
Length
Area
Volume
Angle
Mass
|
| ≡ 60 kg
| = 60 kg
|-----
| quintal (metric) || q
|
| ≡ 100 kg
|-----
| wey ||
| ≡ 252 lb = 18 st
| = 114.305 277 24 kg (variants exist)
|-----
| long quarter||
| ≡ ¼ long tn
| = 254.011 727 2 kg
|-----
| kip || kip
| ≡ 1000 lb av
| = 453.592 37 kg
|-----
| short ton || sh tn
| ≡ 2000 lb
| = 907.184 74 kg
|-----
| tonne (mts unit) || t
|
| ≡ 1000 kg
|-----
| long ton|| long tn or ton
| ≡ 2240 lb
| = 1016.046 908 8 kg
|-----
| barge ||
| ≡ 22 ½ sh tn
| = 20,411.656 65 kg
|{| class="wikitable"
|+ Time, t
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| second || s
|
| (SI base unit)
|-----
| Planck time ||
| ≡ √(Gℏ/c5)
| ≈ 1.351 211 818×10-43 s
|-----
| atomic unit of time || au
| ≡ a0/(α·c)
| ≈ 2.418 884 254×10-17 s
|-----
| svedberg || S
| ≡ 10-13 s
| = 100 fs
|-----
| shake ||
| ≡ 10-8 s
| = 10 ns
|-----
| sigma ||
| ≡ 10-6 s
| = 1 μs
|-----
| jiffy ||
| ≡ 1/60 s
| ≈ 16.666 667 ms
|-----
| jiffy (alternate) ||
| ≡ 1/100 s
| ≈ 10 ms
|-----
| helek ||
| ≡ 1/1080 h
| ≈ 3.333333 s
|-----
| minute || min
|
| ≡ 60 s
|-----
| hour || h
| ≡ 60 min
| = 3600 s
|-----
| day || d
| ≡ 24 h
| = 86 400 s
|-----
| week || wk
| ≡ 7 d
| = 604 800 s
|-----
| fortnight ||
| ≡ 2 wk
| = 1 209 600 s
|-----
| month (hollow) || mo
| ≡ 29 d
| = 2 505 600 s
|-----
| month (full) || mo
| ≡ 30 d
| = 2 592 000 s
|-----
| year (Calendar) || a or y
| ≡ 365 d
| = 31 536 000 s
|-----
| year (Gregorian) || a or y
| ≡ 365.2425 d
| = 31 556 952 s
|-----
| year (Julian) || a or y
| ≡ 365.25 d
| = 31 557 600 s
|-----
| sidereal year || a or y
| ≡ 365.256363 d
| = 31 558 149.76 s
|-----
| lustre; lustrum ||
| ≡ 5 a of 365 d
| = 1.5768×108 s
|-----
| octaeteris ||
| ≡ 8 a of 365 d
| = 2.522 88×108 s
|-----
| decade ||
| ≡ 10 a of 365 d
| = 3.1536×108 s
|-----
| enneadecaeteris; Metonic cycle ||
| ≡ 110 mo (hollow) + 125 mo (full) = 19 a of 365 d
| = 5.996 16×108 s
|-----
| Callippic cycle ||
| ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d
| = 2.398 377 6×109 s
|-----
| century (Calendar) ||
| ≡ 100 a of 365 d
| = 3.1536×109 s
|-----
| century (Julian) ||
| ≡ 100 a of 365.25 d
| = 3.155 76×109 s
|-----
| Hipparchic cycle ||
| ≡ 4 Callippic cycles - 1 d
| = 9.593 424×109 s
|-----
| millennium (Calendar) ||
| ≡ 1000 a of 365 d
| = 3.1536×1010 s
|-----
| millennium (Gregorian) ||
| ≡ 1000 a of 365.2425 d
| = 3.155 695 2×1010 s
|-----
| millennium (Julian) ||
| ≡ 1000 a of 365.25 d
| = 3.155 76×1010 s
|-----
| Sothic cycle ||
| ≡ 1461 a of 365 d
| = 4.607 409 6×1010 s
|{| class="wikitable"
|+ Speed, v
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| metre per second (SI unit)|| m/s
|
| ≡ 1 m/s
|-----
| foot per hour || fph
| ≡ 1 ft/h
| ≈ 8.466 667×10-5 m/s
|-----
| furlong per fortnight ||
| ≡ ½ fur/wk
| ≈ 1.663 095×10-4 m/s
|-----
| inch per minute || ipm
| ≡ 1 in/min
| ≈ 4.23 333×10-4 m/s
|-----
| foot per minute || fpm
| ≡ 1 ft/min
| = 5.08×10-3 m/s
|-----
| inch per second || ips
| ≡ 1 in/s
| = 2.54×10-2 m/s
|-----
| kilometre per hour || km/h
| ≡ 1 km/h
| ≈ 2.777 778×10-1 m/s
|-----
| foot per second || fps
| ≡ 1 ft/s
| = 3.048×10-1 m/s
|-----
| mile per hour || mph
| ≡ 1 mi/h
| = 0.447 04 m/s
|-----
| knot || kn
| ≡ 1 NM/h = 1.852 km/h
| ≈ 0.514 444 m/s
|-----
| knot (Admiralty) || kn
| ≡ 1 NM (Adm)/h = 1.853 184 km/h
| ≈ 0.514 773 m/s
|-----
| mile per minute || mpm
| ≡ 1 mi/min
| = 26.8224 m/s
|-----
| mile per second || mps
| ≡ 1 mi/s
| = 1.609 344 km/s
|-----
| speed of light in vacuum || c
|
| ≡ 2.997 924 58×108 m/s
|{| class="wikitable"
|+ Acceleration, a
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| metre per second squared (SI unit)|| m/s²
|
| ≡ 1 m/s²
|-----
| foot per hour per second || fph/s
| ≡ 1 ft/h·s
| ≈ 8.466 667×10-5 m/s²
|-----
| inch per minute per second || ipm/s
| ≡ 1 in/min·s
| ≈ 4.233 333×10-4 m/s²
|-----
| foot per minute per second || fpm/s
| ≡ 1 ft/min·s
| = 5.08×10-3 m/s²
|-----
| galileo || Gal
| ≡ 1 cm/s²
| = 10-2 m/s²
|-----
| inch per second squared || ips²
| ≡ 1 in/s²
| = 2.54×10-2 m/s²
|-----
| foot per second squared || fps²
| ≡ 1 ft/s²
| = 3.048×10-1 m/s²
|-----
| mile per hour per second || mph/s
| ≡ 1 mi/h·s
| = 4.4704×10-1 m/s²
|-----
| knot per second || kn/s
| ≡ 1 kn/s
| ≈ 5.144 444×10-1 m/s²
|-----
| standard gravity || g
|
| ≡ 9.806 65 m/s²
|-----
| mile per minute per second || mpm/s
| ≡ 1 mi/min·s
| = 26.8224 m/s²
|-----
| mile per second squared || mps²
| ≡ 1 mi/s²
| = 1.609 344×103 m/s²
|{| class="wikitable"
|+ Force, F
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| newton (SI unit) || N
| ≡ kg·m/s²
|
|-----
| atomic unit of force || au
| ≡ me·α²·c²/a0
| ≈ 8.238 722 241×10-8 N
|-----
| dyne (cgs unit) || dyn
| ≡ g·cm/s²
| = 10-5 N
|-----
| gravet ||
| ≡ g × 1 g
| = 9.806 65 mN
|-----
| poundal || pdl
| ≡ 1 lb·ft/s²
| = 0.138 254 954 376 N
|-----
| ounce-force || ozf
| ≡ g × 1 oz
| = 0.278 013 850 953 781 2 N
|-----
| pound-force || lbf
| ≡ g × 1 lb
| = 4.448 221 615 260 5 N
|-----
| kilogram-force; kilopond; grave || kgf; kp
| ≡ g × 1 kg
| = 9.806 65 N
|-----
| sthene (mts unit) || sn
| ≡ 1 t·m/s²
| = 1 kN
|-----
| kip; kip-force || kip; kipf; klbf
| ≡ g × 1000 lb
| = 4.448 221 615 260 5 kN
|-----
| ton-force || tnf
| ≡ g × 1 sh tn
| = 8.896 443 230 521 kN |
|{| class="wikitable"
|+ Pressure, p (lower case)
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| pascal (SI unit) || Pa
| ≡ N/m²
| = kg/m·s²
|-----
| barye (cgs unit) ||
| ≡ 1 dyn/cm²
| = 0.1 Pa
|-----
| poundal per square foot || pdl/sq ft
| ≡ 1 pdl/sq ft
| ≈ 1.488 164 Pa
|-----
| millimetre of water (3.98 °C) || mmH2O
| ≈ 999.972 kg/m³ × 1 mm × g
| = 9.806 38 Pa (= 0.999972 kgf/m²)
|-----
| pound per square foot || psf
| ≡ 1 lb/sq ft × g
| ≈ 47.880 259 Pa
|-----
| centimetre of water (3.98 °C) || cmH2O
| ≈ 999.972 kg/m³ × 1 cm × g
| = 98.0638 Pa
|-----
| torr || torr
| ≡ 101 325/760 Pa
| ≈ 133.322 368 4 Pa
|-----
| millimetre of mercury || mmHg
| ≡ 13 595.1 kg/m³ × 1 mm × g ≈ 1 torr
| = 133.322 387 415 Pa
|-----
| inch of water (3.98 °C) || inH2O
| ≈ 999.972 kg/m³ × 1 in × g
| = 249.082 Pa
|-----
| pièze (mts unit) || pz
| ≡ 1000 kg/m·s²
| = 1 kPa
|-----
| centimetre of mercury || cmHg
| ≡ 13 595.1 kg/m³ × 1 cm × g
| = 1.333 223 874 15 kPa
|-----
| foot of water (3.98 °C) || ftH2O
| ≈ 999.972 kg/m³ × 1 ft × g
| = 2.988 98 kPa
|-----
| inch of mercury || inHg
| ≡ 13 595.1 kg/m³ × 1 in × g
| = 3.386 388 640 341 kPa
|-----
| pound per square inch || psi
| ≡ 1 lb × g / 1 sq in
| ≈ 6.894 757×103 Pa
|-----
| foot of mercury || ftHg
| ≡ 13 595.1 kg/m³ × 1 ft × g
| = 40.636 663 684 091 9 kPa
|-----
| short ton per square foot ||
| ≡ 1 sh tn × g / 1 sq ft
| ≈ 95.760 518 kPa
|-----
| atmosphere (technical) || atm
| ≡ 1 kgf/cm²
| = 98.0665 kPa
|-----
| bar || bar
|
| ≡ 105 Pa
|-----
| atmosphere (standard) || atm
|
| ≡ 101 325 Pa
|-----
| kip per square inch || ksi
| ≡ 1 kipf/sq in
| ≈ 6.894757 MPa
|-----
| kilogram-force per square millimetre || kgf/mm²
| ≡ 1 kgf/mm²
| = 9.806 65 MPa
|{| class="wikitable"
|+ Energy, E, W
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| joule (SI unit) || J
| ≡ N·m = W·s = V·A·s
| = kg·m²/s²
|-----
| electronvolt || eV
| ≡ e × 1 V
| ≈ 1.602 176×10-19 J
|-----
| rydberg || Ry
| ≡ R∞·ℎ·c
| ≈ 2.179 872×10-18 J
|-----
| hartree || Eh
| ≡ me·α²·c² (= 2 Ry)
| ≈ 4.359 744×10-18 J
|-----
| atomic unit of energy || au
| ≡ Eh ≈ 4.359 744×10-18 J
|-----
| erg (cgs unit) || erg
| ≡ 1 g·cm²/s²
| = 10-7 J
|-----
| foot-poundal || ft pdl
| ≡ 1 lb·ft²/s²
| = 4.214 011 009 380 48×10-2 J
|-----
| cubic centimetre of atmosphere; standard cubic centimetre || cc atm; scc
| ≡ 1 atm × 1 cm³
| = 0.101 325 J
|-----
| inch-pound force || in lbf
| ≡ g × 1 lb × 1 in
| = 0.112 984 829 027 616 7 J
|-----
| foot-pound force || ft lbf
| ≡ g × 1 lb × 1 ft
| = 1.355 817 948 331 400 4 J
|-----
| calorie (20 °C) || cal20 °C
|
| ≈ 4.1819 J
|-----
| calorie (thermochemical) || calth
|
| ≡ 4.184 J
|-----
| calorie (15 °C) || cal15 °C
|
| ≡ 4.1855 J
|-----
| calorie (International Table) || calIT
|
| ≡ 4.1868 J
|-----
| calorie (mean) || calmean
|
| ≈ 4.190 02 J
|-----
| calorie (3.98 °C) || cal3.98 °C
|
| ≈ 4.2045 J
|-----
| litre-atmosphere || l atm; sl
| ≡ 1 atm × 1 L
| = 101.325 J
|-----
| gallon-atmosphere (U.S.) || US gal atm
| ≡ 1 atm × 1 gal (US)
| = 383.556 849 013 8 J
|-----
| gallon-atmosphere (Imperial) || US gal atm
| ≡ 1 atm × 1 gal (Imp)
| = 460.632 569 25 J
|-----
| British thermal unit (thermochemical) || BTUth
| ≡ 1 lb/g × 1 calth × 1 °F/°C = 9.489 152 380 4 ÷ 9 kJ
| ≈ 1.054 350 kJ
|-----
| British thermal unit (ISO) || BTUISO
|
| ≡ 1.0545 kJ
|-----
| British thermal unit (63 °F) || BTU63 °F
|
| ≈ 1.0546 kJ
|-----
| British thermal unit (60 °F) || BTU60 °F
|
| ≈ 1.054 68 kJ
|-----
| British thermal unit (59 °F) || BTU59 °F
|
| ≡ 1.054 804 kJ
|-----
| British thermal unit (International Table) || BTUIT
| ≡ 1 lb/g × 1 calIT × 1 °F/°C
| = 1.055 055 852 62 kJ
|-----
| British thermal unit (mean) || BTUmean
|
| ≈ 1.055 87 kJ
|-----
| British thermal unit (39 °F) || BTU39 °F
|
| ≈ 1.059 67 kJ
|-----
| Celsius heat unit (International Table) || CHUIT
| ≡ 1 BTUIT × 1 °C/°F
| = 1.899 100 534 716 kJ
|-----
| cubic foot of atmosphere; standard cubic foot || cu ft atm; scf
| ≡ 1 atm × 1 ft³
| = 2.869 204 480 934 4 kJ
|-----
| kilocalorie; large calorie || kcal; Cal
| ≡ 1000 calIT
| = 4.1868 kJ
|-----
| cubic yard of atmosphere; standard cubic yard || cu yd atm; scy
| ≡ 1 atm × 1 yd³
| = 77.468 520 985 228 8 kJ
|-----
| cubic foot of natural gas ||
| ≡ 1000 BTUIT
| = 1.055 055 852 62 MJ
|-----
| horsepower-hour || hp·h
| ≡ 1 hp × 1 h
| = 2.6845 MJ
|-----
| Board of Trade Unit; kilowatt-hour || B.O.T.U.; kW·h
| ≡ 1 kW × 1 h
| = 3.6 MJ
|-----
| thermie || th
| ≡ 1 McalIT
| = 4.1868 MJ
|-----
| therm (U.S.) ||
| ≡ 100 000 BTU59 °F
| = 105.4804 MJ
|-----
| therm (E.C.) ||
| ≡ 100 000 BTUIT
| = 105.505 585 262 MJ
|-----
| ton of TNT || tTNT
| ≡ 1 Gcalth
| = 4.184 GJ
|-----
| barrel of oil equivalent || bboe
| ≈ 5.8 MBTU59 °F
| ≈ 6.12 GJ
|-----
| ton of coal equivalent || TCE
| ≡ 7 Gcalth
| = 29.3076 GJ
|-----
| ton of oil equivalent || TOE
| ≡ 10 Gcalth
| = 41.868 GJ
|-----
| quad ||
| ≡ 1015 BTUIT
| = 1.055 055 852 62 EJ
|{| class="wikitable"
|+ Power, P
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| watt (SI unit) || W
| ≡ J/s = N·m/s
| = kg·m²/s³
|-----
| lusec || lusec
| ≡ 1 L·µmHg/s
| ≈ 1.333 224×10-4 W
|-----
| foot-pound-force per hour || ft lbf/h
| ≡ 1 ft lbf/h
| ≈ 3.766 161×10-4 W
|-----
| atmosphere cubic centimetre per minute || atm ccm
| ≡ 1 atm × 1 cm³/min
| = 1.688 75×10-3 W
|-----
| foot-pound-force per minute || ft lbf/min
| ≡ 1 ft lbf/min
| = 2.259 696 580 552 334×10-2 W
|-----
| atmosphere–cubic centimetre per second || atm ccs
| ≡ 1 atm × 1 cm³/s
| = 0.101 325 W
|-----
| BTU (International Table) per hour || BTUIT/h
| ≡ 1 BTUIT/h
| ≈ 0.293 071 W
|-----
| atmosphere–cubic foot per hour || atm cfh
| ≡ 1 atm × 1 cu ft/h
| = 0.797 001 244 704 W
|-----
| foot-pound-force per second || ft lbf/s
| ≡ 1 ft lbf/s
| = 1.355 817 948 331 400 4 W
|-----
| litre-atmosphere per minute || L·atm/min
| ≡ 1 atm × 1 L/min
| = 1.688 75 W
|-----
| calorie (International Table) per second || calIT/s
| ≡ 1 calIT/s
| = 4.1868 W
|-----
| BTU (International Table) per minute || BTUIT/min
| ≡ 1 BTUIT/min
| ≈ 17.584 264 W
|-----
| atmosphere-cubic foot per minute || atm·cfm
| ≡ 1 atm × 1 cu ft/min
| = 47.820 074 682 24 W
|-----
| square foot equivalent direct radiation || sq ft EDR
| ≡ 240 BTUIT/h
| ≈ 70.337 057 W
|-----
| litre-atmosphere per second || L·atm/s
| ≡ 1 atm × 1 L/s
| = 101.325 W
|-----
| horsepower (metric) || hp
| ≡ 75 m kgf/s
| = 735.498 75 W
|-----
| horsepower (European electrical) || hp
| ≡ 75 kp·m/s
| = 736 W
|-----
| horsepower (Imperial mechanical) || hp
| ≡ 550 ft lbf/s
| = 745.699 871 582 270 22 W
|-----
| horsepower (Imperial electrical) || hp
|
| ≡ 746 W
|-----
| ton of air conditioning ||
| ≡ 1 t × 1005 J/kg × 1 °F/K ÷ 10 min
| = 844.2 W
|-----
| poncelet || p
| ≡ 100 m kgf/s
| = 980.665 W
|-----
| BTU (International Table) per second || BTUIT/s
| ≡ 1 BTUIT/s
| = 1.055 055 852 62×10+3 W
|-----
| atmosphere-cubic foot per second || atm cfs
| ≡ 1 atm × 1 cu ft/s
| = 2.869 204 480 934 4×10+3 W
|-----
| ton of refrigeration (IT) ||
| ≡ 1 BTUIT × 1 sh tn/lb ÷ 10 min/s
| ≈ 3.516 853×10+3 W
|-----
| ton of refrigeration (Imperial) ||
| ≡ 1 BTUIT × 1 lng tn/lb ÷ 10 min/s
| ≈ 3.938 875×10+3 W
|-----
| boiler horsepower || bhp
| ≈ 34.5 lb/h × 970.3 BTUIT/lb
| ≈ 9.810 657×10+3 W
|{| class="wikitable"
|+ Action, Angular momentum, L, J
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| SI unit || J·s
|
| ≡ kg·m²/s
|-----
| atomic unit of action || au
| ≡ ℏ = ℎ/2π
| ≈ 1.054 571 596×10-34 J·s
|-----
| cgs unit || erg·s
|
| = 10-7 J·s
|{| class="wikitable"
|+ Electric current, I
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| ampere || A
|
| (SI base unit)
|-----
| esu per second; statampere (cgs unit) || esu/s
| ≡ (0.1 A·m/s)/c
| ≈ 3.335 641×10-10 A
|-----
| electromagnetic unit; abampere (cgs unit) || abamp
|
| ≡ 10 A
|{| class="wikitable"
|+ Electric charge, Q
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| coulomb (SI unit) || C
|
| ≡ A·s
|-----
| atomic unit of charge || au
| ≡ e
| ≈ 1.602 176 462×10-19 C
|-----
| statcoulomb; franklin; electrostatic unit (cgs unit) || statC; Fr; esu
| ≡ (0.1 A·m)/c
| ≈ 3.335 641×10-10 C
|-----
| abcoulomb; electromagnetic unit (cgs unit) || abC; emu
|
| ≡ 10 C
|-----
| faraday || F
| ≡ 1 mol × NA·e
| ≈ 96,485.3383 C
|{| class="wikitable"
|+ Voltage, Electromotive force, U
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| volt (SI unit) || V
|
| ≡ kg·m²/A·s³
|-----
| abvolt (cgs unit) || abV
|
| ≡ 1×10-8 V
|-----
| statvolt (cgs unit) || statV
| ≡ c·(1 μJ/A·m)
| = 299.792 458 V
|{| class="wikitable"
|+ Electrical resistance, R
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| ohm (SI unit) || Ω
| ≡ V/A
| = kg·m²/A²s³
|{| class="wikitable"
|+ Dynamic viscosity, η
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| pascal second (SI unit) || Pa·s
| ≡ N·s/m²
| = kg/m·s
|-----
| poise (cgs unit) || P
|
| ≡ 10-1 Pa·s
|{| class="wikitable"
|+ Kinematic viscosity, ν
!Name of unit
!Symbol
!Definition
!Relation to SI units
|-----
| SI unit || m²/s
|
| ≡ m²/s
|-----
| stokes (cgs unit) || St
|
| ≡ 10-4 m²/s
|{| class="wikitable"
|+ Temperature, T
!Name of unit
!Symbol
!Relation to SI units
!Relation to °C
|-----
| kelvin || K
| SI base unit
| T[K] = T[°C] + 273.15
|-----
| degree Celsius || °C
| T[°C] = T[K] − 273.15
|
|-----
| degree Rankine || °R; °Ra
| T[°Ra] = 1.8 × T[K]
|
|-----
| degree Fahrenheit || °F
| T[°F] = T[K] × 1.8 − 459.67
| T[°F] = 1.8 × T[°C] + 32
|{
Metre:This article is about the unit of length. For other uses of metre or meter, see meter (disambiguation).
The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. It is defined as the length of the path travelled by light in absolute vacuum during a time interval of 1/299,792,458 of a second.
Adding SI prefixes to metre creates multiples and submultiples; for example kilometre (1000 metres; kilo- = 1000) and millimetre (one thousandth of a metre; milli- = 1 / 1 000).
Conversions
1 metre is equivalent to:
- exactly 1/0.9144 yards (approximately 1.0936 yards)
- exactly 1/0.3048 feet (approximately 3.2808 feet)
- exactly 10000/254 inches (approximately 39.370 inches)
History
The word metre is from the Greek metron (μετρον), "a measure" via the French mètre. Its first recorded usage in English is from 1797.
In the 18th century, there were two favoured approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a pendulum with a half-period of one second. The other suggested defining the metre as one ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth). In 1791, the French Academy of Sciences selected the meridional definition over the pendular definition because of the slight variation of the force of gravity over the surface of the earth, which affects the period of a pendulum. In 1793, France adopted the metre, with this definition, as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the earth, this length became the standard. So, the circumference of the Earth through the poles is approximately forty million metres.
Earth in a vacuum.]]
In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The Metre Convention (Convention du Mètre) of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM: Bureau International des Poids et Mesures) to be located in Sèvres, France. This new organisation would preserve the new prototype metre and kilogram when constructed, distribute national metric prototypes, and would maintain comparisons between them and non-metric measurement standards. This organisation created a new prototype bar in 1889 at the first General Conference on Weights and Measures (CGPM: Conférence Générale des Poids et Mesures), establishing the International Prototype Metre as the distance between two lines on a standard bar of an alloy of ninety percent platinum and ten percent iridium, measured at the melting point of ice.
In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh CGPM defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.
To further reduce uncertainty, the seventeenth CGPM of 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of time and the speed of light:
:The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
Note that this definition exactly fixes the speed of light in a vacuum at 299,792,458 metres per second. Definitions based on the physical properties of light are more precise and reproducible because the properties of light are considered to be universally constant.
Timeline of definition
- 1790 May 8 — The French National Assembly decides that the length of the new metre would be equal to the length of a pendulum with a half-period of one second.
- 1791 March 30 — The French National Assembly accepts the proposal by the French Academy of Sciences that the new definition for the metre be equal to one ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth).
- 1795 — Provisional metre bar constructed of brass.
- 1799 December 10 — The French National Assembly specifies that the platinum metre bar, constructed on 23 June 1799 and deposited in the National Archives, as the final standard.
- 1889 September 28 — The first CGPM defines the length as the distance between two lines on a standard bar of an alloy of platinum with ten percent iridium, measured at the melting point of ice.
- 1927 October 6 — The seventh CGPM adjusts the definition of the length to be the distance, at 0 °C, between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard atmosphere of pressure and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other.
- 1960 October 20 — The eleventh CGPM defines the length to be equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.
- 1983 October 21 — The seventeenth CGPM defines the length to be distance travelled by light in vacuum during a time interval of 1/299 792 458 of a second.
See also
- Metric system
- SI
- SI prefix
- Conversion of units for comparisons with other units
- Orders of magnitude (length)
- Speed of light
External links
- [http://www.unitconversion.org/unit_converter/length.html?unit=meter&value=1 Length Converter: convert metre to other units, such as yard, mile, and so on]
- [http://physics.nist.gov/cuu/Units/meter.html History of the metre at the U.S. National Institute of Standards and Technology (NIST)]
- [http://www.mel.nist.gov/div821/museum/timeline.htm Timeline of history of the metre at the NIST]
- [http://www1.bipm.org/en/scientific/length/ Bureau International des Poids et Measures - Lengths]
Category:SI base units
Category:Units of length
ko:미터
ms:Meter
ja:メートル
simple:Metre
th:เมตร
HectareA hectare (symbol ha) is a unit of area, commonly used for measuring land area. It is not an SI unit, but it is accepted (although not encouraged) for use with the SI. The SI unit of area is the square metre.
Definition
:1 hectare = 10,000 square metres = (100 metres)2 = 100 metres × 100 metres.
Thus a hectare is the area of a square plot of land when the length of each of the four sides of the square is 100 metres.
The name is a contraction of the SI prefix hecto + are; a hectare is 100 ares. An are is the area of a 10 metre by 10 metre square.
Explanation
The hectare is common in domains such as agriculture, forestry, and town planning in many countries. It is rarely used in the United States. In a few other countries that have only partially or recently adopted the metric system (e.g. the United Kingdom) it is only used in technical contexts.
Conversions
One hectare is equivalent to:
Metric
- 100 ares
- 10 000 square metres = 100 metres × 100 metres
- 1 square hectometre (a square with sides 100 metres long)
- 0.01 square kilometres
- 10 decares
- 2.471 053 8 international acres
- 2.471 043 9 U.S. survey acres
- 107,639 square feet
- 0.00386 102 square miles (statute)
Other
- 15 mus (Chinese)
- 10 dunams (Middle East)
- 6.25 rai (Thai)
See also
- Orders of magnitude
- conversion of units
- 1 E4 m² for further comparisons
External links
- [http://www.bipm.org/en/si/si_brochure/chapter4/4-1.html Official SI website: Table 8. Other non-SI units currently accepted for use with the International System Their use is not encouraged.]
- [http://www.ex.ac.uk/trol/scol/ccarea.htm Conversion Calculator for Units of AREA]
Category:Units of area
als:Hektar
ja:ヘクタール
Rod (unit)A rod is a unit of length, equal to 5.5 yards or 16.5 feet (5.0292 metres in SI units). It is the same length as a perch and a pole.
The length is equal to the standardized length of the ox-goad used by medieval English ploughmen; fields were measured in acres which were one chain (four rods) by one furlong (in the United Kingdom, ten chains).
Because the furlong was "One Plough's Furrow Long" and a furrow was the length a plough team was to be driven without resting, the length of the furlong and the acre vary regionally, nominally due to differing soil types. In England the acre was 4,840 square yards, but in Scotland it was 6,150 square yards and in Ireland 7,840 square yards. In all three countries, fields were divided in acres and thus the furlong became a measure commonly used in horse racing, archery, and civic planning.
The rod is still in use as a unit of measure in recreational canoeing. In particular, canoeing maps measure portages (overland paths where canoes must be carried) in rods. This is thought to persist due to the rod approximating the length of a typical canoe.
The lengths of the perch and chain were standardized in 1607 by Edmund Gunter.
Notes
# A perch is also a unit of area of land = 1 square rod, and a unit of cubic measure of stonework, usually = 16.5 feet by 1 foot by 1.5 feet = 24.75 cubic feet.
See also
- furlong
- perch (volume) for a related unit of volume with the same name.
Popular culture and trivia
- In the episode of The Simpsons entitled ‘A Star is Burns’, Grampa Simpson uttered: “My car gets forty rods to the hogshead, and that's the way I likes it!” That translates into 432 (beer) or 504 (wine) gallons per mile, or about 1.2 litres per metre!
Category:Imperial units
Category:Units of length
Category:Customary units in the United States
RoodRood is an archaic word for “pole”, from Anglo-Saxon rōd “pole”, specifically “crucifix”, from Proto-Germanic
- rodo, cognate to Old Saxon rōda, Old High German ruoda “rod”; the relation of rood to rod, from Anglo-Saxon rodd “pole” is unclear; the latter was perhaps influenced by Old Norse rudda “club”).
Specifically, rood is an old English unit of area, equal to quarter an acre, i.e. 10 890 square feet or 1011.7141056 m² (for the international inch) or about 10.1 are. A rectangular area with edges of one furlong and one rod respectively is one rood, as is an area consisting of 40 square rods. Confusingly called an acre in some ancient contexts. The rood is an important measure in surveying on account of its easy conversion with the acre. In provincial England, a rood was also a measure of length, corresponding to five and a half yards.
In the meaning “crucifix”, rood may refer to a representation in sculpture or in painting of the cross with Christ hanging on it. It remains in use in some names, like Holyrood Palace and Dream of the Rood. The phrase "by the rood" was used in swearing, e.g. “No, by the rood, not so” in Shakespeare’s Hamlet (Act 3, Scene 4).
In church architecture a rood screen is a wooden or stone screen, usually separating the chancel or choir from the nave. The screen may be elaborately carved and may have been painted. It supported a large cross or crucifix, though in England these were often destroyed by Puritans during the English Civil War; at the same time many rood screens were themselves destroyed. Some rood screens incorporated a narrow singing gallery called a rood loft. The rood stair which gave access to the gallery is often the only remaining sign of the rood loft.
Reference
Pevsner, Nikolaus, The Buildings of England, Penguin Books (original series, 1951–1974)
Category:Units of area
Category:Anglo-Saxon England
Category:Architecture
See also
- Rood (Scots)
Furlong]
A furlong is a measure of distance within Imperial units and U.S. customary units. Although its definition has varied historically, in modern terms it equals 660 feet or 220 yards, and is therefore equal to 201.168 metres. There are ten chains in a furlong and eight furlongs in a mile. The name "furlong" derives from the Old English words furh (furrow) and lang (long). It originally referred to the length of the furrow in one acre of a ploughed open field (a medieval communal field which was divided into strips). The system of long furrows arose because turning a team of oxen pulling a heavy plough was difficult. This offset the drainage advantages of short furrows and meant furrows were made as long as possible. For this reason, it was once also called an acre's length.
Distances for thoroughbred horse races in the United Kingdom, Ireland and the United States are given alternately in miles and furlongs ([http://www.sportinglife.com/racing/goodwood/course/ example]), but the unit is otherwise no longer in common use — and even in that discipline its usage is confined mainly to denoting distances of less than one mile. Its official use was abolished in the United Kingdom under the Weights and Measures Act 1985, which also abolished from official use many other traditional units of measurement.
Coincidentally, 5 furlongs is 1005.84 metres (exactly) and is therefore approximately 1 kilometre.
Trivia
An absurd unit of speed often misquoted is the furlong per fortnight, which converts to:
- 0.0001663095 metre per second or roughly one centimetre per minute (in SI units)
- 0.0005456349 feet per second (in Imperial units)
Thus:
- a car travelling at 60 km/h (37 mph) is travelling at a speed of 100,214.7 furlongs per fortnight;
- a Boeing 737 cruising at 420 knots or 216.2 m/s (i.e. typical 0.8 Mach cruise) is travelling at 1,300,013.7 furlongs per fortnight;
- the speed of light in vacuum is approximately 1.803
- 1012 furlongs per fortnight;
- one furlong per fortnight is 0.166 millimetres per second, which would be barely noticeable to the naked eye.
The city of Chicago's numbering system allots a measure of 800 to each mile. Logically, streets were subsequently laid out 8 to the mile. This means that every block in a typical Chicago neighborhood (in either North/South or East/West direction but rarely both) is precisely one furlong.
Category:Units of length
Category:Imperial units
Category:Customary units in the United States
ja:ハロン (単位)
Chain (length)The chain is an English unit of length. It is defined as 66 feet (20.1168 metres). It is also known as the surveyor's chain, Gunter's chain or land chain.
Conversions
1 chain is equivalent to:
- 66 feet (exactly)
- 22 yards (exactly)
- 4 rods (exactly)
- 4 poles (exactly)
- 4 perches (exactly)
- 100 links
- 10 chains = 1 furlong
- 80 chains = 1 mile
Since the width of an acre was defined as one chain (with a length of one furlong), it was also known as an acre's breadth.
acre]
History
The term chain derives from the device commonly used for measurement of land in the past — a chain of 100 links, the Gunter's chain being the most common. The links were about eight inches long, made of heavy gauge wire, with a loop at each end. The links were joined end to end to create the chain by three rings between the links. This enabled the chain to be folded up, link by link, until all 100 were in a bundle which could be held in the hand. At each end were brass handles and the full chain measurement was between the outside extremities of the brass handles with the chain at full stretch on flat ground. If the chain had been folded correctly, an experienced chainman (surveyor's assistant) could fling the bundle out and it would unfold neatly with no snags. Another chainman would grab the handle, flick the chain to get it straight and then be ready to take the measurement. Long distances would be measured in bays of one chain, the actual chain being dragged forward for each bay.
With so many links in the chain there were many wearing surfaces and chains commonly were longer than the designated length. Also some surveyors added an extra link, so that their surveys always included a greater physical area than the actual measurements indicated (the landowners weren't going to complain!). When retracing old surveys with modern equipment a surveyor will almost always find his measurements between monuments are longer than the originals.
The unit was once important in everyday life, being one of the fundamental units of Imperial system in the United Kingdom and its colonies, and was used to some extent in engineering and surveying in the U.S.
In Britain, it was commonly used in the railway industry (where the measure is still in widespread use). Mapping by the Ordinance Survey (Britain's national mapping organisation) began in the early 19th century using the chain as the basic unit of measurement. All map scales at that time were expressed as a relative fraction of a chain or a mile (e.g. a one inch to ten chain scale was equivalent to 1:7920 or eight inches to a mile).
The use of the chain was once very common in laying out townships and mapping the U.S. along the train routes in the 19th century. In the U.S. a federal law was passed in 1785 (the Public Land Survey Ordinance) that all official government surveys must be done with a Gunter's chain (also referred to as the "surveyor's chain").
American surveyors sometimes used a longer chain of 100 feet (30.48 m), known as the engineer's chain or Ramsden's chain. In Texas, the vara chain of 20 varas (55.556 ft) was used in surveying Spanish land grants.
In agriculture, measuring wheels with a circumference of 0.1 chain are still common and readily available in the United States and Canada, at least. For a rectangular tract, multiply the number of turns of one of these wheels for each side, then divide by 1000 to get the area in acres.
The chain also survives, in fact if not always in name, in two other specific contexts.
- It is the length of the pitch, between the wickets, in cricket.
- It lies at the origin of the definition of an acre as 4840 square yards. The original acre was an area of land suitable for ploughing in a defined time, and was therefore not square; it measured one chain by one furlong (10 square chains).
In the laying out of towns in Australia and New Zealand, most building lots in the past were a quarter of an acre, measuring one chain by two and a half chains, and other lots would be multiples or fractions of a chain. The city of Melbourne is a classic example: surveyor Robert Hoddle divided the city into 24 ten-chain blocks, which still serve as the basic grid of the city. The street frontages of many houses in these countries are one chain wide—roads were almost always one chain wide (20.117 m) in urban areas, sometimes one and a half or two chains (30.2 m or 40.2 m). Laneways would be half a chain (10.1 m). In rural areas the roads were wider, up to 10 chains (201 m) where a stock route was required.
External links
- [http://www.pballew.net/arithm16.html#gunter Math Words]
- [http://www.unc.edu/~rowlett/units/introd.html How Many? A Dictionary of Units of Measurement], Russ Rowlett
- [http://www.orbitals.com/self/survey/chain/chain.html How to make a Gunter's Chain]
Category:Units of length
Category:Imperial units
Category:Surveying
Category:Customary units in the United States
Metre:This article is about the unit of length. For other uses of metre or meter, see meter (disambiguation).
The metre (Commonwealth English) or meter (American English) (symbol: m) is the SI base unit of length. It is defined as the length of the path travelled by light in absolute vacuum during a time interval of 1/299,792,458 of a second.
Adding SI prefixes to metre creates multiples and submultiples; for example kilometre (1000 metres; kilo- = 1000) and millimetre (one thousandth of a metre; milli- = 1 / 1 000).
Conversions
1 metre is equivalent to:
- exactly 1/0.9144 yards (approximately 1.0936 yards)
- exactly 1/0.3048 feet (approximately 3.2808 feet)
- exactly 10000/254 inches (approximately 39.370 inches)
History
The word metre is from the Greek metron (μετρον), "a measure" via the French mètre. Its first recorded usage in English is from 1797.
In the 18th century, there were two favoured approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a pendulum with a half-period of one second. The other suggested defining the metre as one ten-millionth of the length of the earth's meridian along a quadrant (one-fourth the polar circumference of the earth). In 1791, the French Academy of Sciences selected the meridional definition over the pendular definition because of the slight variation of the force of gravity over the surface of the earth, which affects the period of a pendulum. In 1793, France adopted the metre, with this definition, as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the earth, this length became the standard. So, the circumference of the Earth through the poles is approximately forty million metres.
Earth in a vacuum.]]
In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The Metre Convention (Convention du Mètre) of 1875 mandated the establishment of a permanent International Bureau of Weights and Measures (BIPM: Bureau International des Poids et Mesures) to be located in Sèvres, France. This new organisation would preserve the new prototype metre and kilogram when constructed, distribute national metric prototypes, and would maintain comparisons between them and non-metric measurement standards. This organisation created a new prototype bar in 1889 at the first General Conference on Weights and Measures (CGPM: Conférence Générale des Poids et Mesures), establishing the International Prototype Metre as the distance between two lines on a standard bar of an alloy of ninety percent platinum and ten percent iridium, measured at the melting point of ice.
In 1893, the standard metre was first measured with an interferometer by Albert A. Michelson, the inventor of the device and an advocate of using some particular wavelength of light as a standard of distance. By 1925, interferometry was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh CGPM defined the metre in the new SI system as equal to 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.
To further reduce uncertainty, the seventeenth CGPM of 1983 replaced the definition of the metre with its current defini | |
