Imperial units
From 1ste Gimnechiske Wiki
This is derived from the standard made up by the Imperial Weight and Measures Office, a standardization program started by the British empire (thereof the name), but since this system was constantly adjusted, and adopted various places in various ways, the modern usage of it is divided between the Imperial standard (British) and the US Standard (self explanatory). I will focus on the British where it is different.
Contents |
Length
| Unit | Relative to previous | Feet | Millimetres | Metres | Notes |
|---|---|---|---|---|---|
| thou | 1⁄12000 | 0.0254 | 25.4 μm The unit is known as a mil in the United States. <ref> url=http://ts.nist.gov/WeightsAndMeasures/Publications/upload/h4402_appenc.pdf </ref> | ||
| inch | 1000 thou | 1⁄12 | 25.4 | ||
| foot | 12 inches | 1 | 304.8 | 0.3048 | |
| yard | 3 feet | 3 | 914.4 | 0.9144 | Defined as exactly 0.9144 metres since 1956. |
| furlong | 220 yards | 660 | 201.168 | ||
| mile | 8 furlongs | 5280 | 1609.344 | ||
| league | 3 miles | 15,840 | 4828.032 | No longer an official unit in any nation. | |
| Maritime units | |||||
| fathom | 6.08 or 6 <ref> The exact figure was 6.08 feet but 6 feet was in use in practice. </ref> | 1,853.184 | 1.853184 |
The British Admiralty in practice used a fathom as 6 feet. This was despite its being 1⁄1000 of a nautical mile (i.e. 6.08 feet) until 1970, when the international nautical mile of exactly 1852 metres was adopted. The commonly accepted definition of a fathom was always 6 feet. The conflict was inconsequential in determining depth as Admiralty nautical charts used feet as depths below 5 fathoms on older imperial charts. Today all charts worldwide are metric, except for USA Hydrographic Office charts, which use feet for all depth ranges. | |
| cable | ~100 fathoms | 608 | 185.3184 | One tenth of a nautical mile. When in use it was approximated colloquially as 100 fathoms. | |
| nautical mile | 10 cables | 6,080 | 1,853.184 | Used to measure distances at sea. This value referred to the British nautical (Admiralty) mile of 6,080 ft; the modern international mile is slightly different. | |
| Gunter's survey units (17th century onwards) | |||||
| link | 66⁄100 | 201.168 | 0.201168 | ||
| pole | 25 links | 66⁄4 | 5029.2 | 5.0292 | The pole is also called rod or perch. |
| chain | 4 poles | 66 | 20.1168 | 1⁄10 furlong | |
Until the adoption of the international definition of 1852 metres in 1970, the British nautical mile was defined as 6,080 feet. 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).
Area
| Unit | Relation to units of length | Square feet | Square rods | Square miles | Square metres | Hectares | Notes |
|---|---|---|---|---|---|---|---|
| perch | 1 rod × 1 rod | 272.25 | 1 | 1⁄10240 | 25.29285264 | 0.002529 | The rood is also called a rod. <ref> http://janus.lib.cam.ac.uk/db/node.xsp?id=EAD%2FGBR%2F0272%2FKC%2FKCAR%2F6%2F2;recurse=1 </ref> <ref> http://janus.lib.cam.ac.uk/db/node.xsp?id=EAD%2FGBR%2F0272%2FKC%2FKCAR%2FMON%2F38 </ref> |
| rood | 1 furlong × 1 rod <ref> http://ts.nist.gov/WeightsAndMeasures/Publications/upload/h4402_appenc.pdf </ref> | 10,890 | 40 | 1⁄2560 | 1011.7141056 | 0.1012 | Although the proper term is square rod, for centuries this unit has been called a pole or perch or, more properly square pole or square perch. |
| acre | 1 furlong × 1 chain | 43,560 | 160 | 1⁄640 | 4046.8564224 | 0.4047 | |
| Note: All equivalences are exact except the hectares, which are accurate to four significant figures. | |||||||
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 Hg 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 4.545 964 591 L, or 277.420 cu in. The Weights and Measures Act of 1985 switched to a gallon of exactly 4.546 09 L (approximately 277.4 cu in).<ref>Sizes.com</ref>
| Unit | Imperial ounce | Imperial pint | Millilitres | Cubic inches | US ounces | US pints |
|---|---|---|---|---|---|---|
| fluid ounce (fl oz) | 1 | 1⁄20 | 28.4130625 | |||
| gill | 5 | 1⁄4 | 142.0653125 | |||
| pint (pt) | 20 | 1 | 568.26125 | |||
| quart (qt) | 40 | 2 | 1136.5225 | |||
| gallon (gal) | 160 | 8 | 4546.09 | |||
| Note: The millilitre equivalences are exact whereas the conversions to cubic-inch and US measures are correct to five significant figures. | ||||||
For a comparison to the US customary system see the article on Comparison of the imperial and US customary measurement systems.
Mass
In the 19th and 20th centuries Britain has used three different systems for mass and weight:<ref>The distinction between mass and weight is not always clearly drawn. In certain contexts the term pound may refer to a unit of force rather than mass.</ref>
- 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 troy pound (373.2417216) was made the primary unit of mass by the 1824 Act， however, its use was abolished in Britain on 6 January 1879, making the Avoirdupois pound the primary unit of mass with only the troy ounce (31.1034768) 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.
| Unit | Pounds | Grams | Kilograms | Notes |
|---|---|---|---|---|
| grain | 1⁄7000 | 0.06479891 | Exactly 64.79891 milligrams. | |
| drachm | 1⁄256 | 1.7718451953125 | ||
| ounce (oz) | 1⁄16 | 28.349523125 | ||
| pound (lb) | 1 | 453.59237 | 0.45359237 | Exactly 453.59237 grams by definition. |
| stone (st) | 14 | 6350.29318 | 6.35029318 | A person's weight is often quoted in stone and pounds in English-speaking countries, with the exception of the United States and Canada, where it is usually quoted in pounds. |
| quarter | 28 | 12.70058636 | A "quarter" was also commonly used to refer to a quarter of a pound in a retail context. | |
| hundredweight (cwt) | 112 | 50.80234544 | ||
| ton (t) | 2240 | 1016.0469088 | 20 hundredweights in both systems, US hundredweight being lighter. |
The British ton (the long ton), is 2240 pounds, 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). Each is divided into 20 hundredweights (cwt), the British hundredweight of 112 pounds being 12% heavier than the American hundredweight.
