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English units of measurement

English units of measurement, principal system of weights and measures used in a few nations, the only major industrial one being the United States. It actually consists of two related systems—the U.S. Customary System of units, used in the United States and dependencies, and the British Imperial System. The names of the units and the relationships between them are generally the same in both systems, but the sizes of the units differ, sometimes considerably.

Customary Units of Weights and Measures

Units of Weight

The pound (lb) is the basic unit of weight (which is proportional to mass). Within the English units of measurement there are three different systems of weights. In the avoirdupois system, the most widely used of the three, the pound is divided into 16 ounces (oz) and the ounce into 16 drams. The ton, used to measure large masses, is equal to 2,000 lb (short ton) or 2,240 lb (long ton). In Great Britain the stone, equal to 14 lb, is also used. The troy system (named for Troyes, France, where it is said to have originated) is used only for precious metals. The troy pound is divided into 12 ounces and the troy ounce into 20 pennyweights or 480 grains; the troy pound is thus 5,760 grains. The grain is also a unit in the avoirdupois system, 1 avoirdupois pound being 7,000 grains, so that the troy pound is 5,760/7,000 of an avoirdupois pound. Apothecaries' weights are based on troy weights; in addition to the pound, ounce, and grain, which are equal to the troy units of the same name, other units are the dram (1/8 oz) and the scruple (1/24 oz or 1/3 dram).

Units of Length and Area

The basic unit of length is the yard (yd); fractions of the yard are the inch (1/36 yd) and the foot (1/3 yd), and commonly used multiples are the rod (51-2 yd), the furlong (220 yd), and the mile (1,760 yd). The acre, equal to 4,840 square yards or 160 square rods, is used for measuring land area.

Units of Liquid Measure

For liquid measure, or liquid capacity, the basic unit is the gallon, which is divided into 4 quarts, 8 pints, or 32 gills. The U.S. gallon, or wine gallon, is 231 cubic inches (cu in.); the British imperial gallon is the volume of 10 lb of pure water at 62℉ and is equal to 277.42 cu in. The British units of liquid capacity are thus about 20% larger than the corresponding American units. The U.S. fluid ounce is 1/16 of a U.S. pint; the British unit of the same name is 1/20 of an imperial pint and is thus slightly smaller than the U.S. fluid ounce.

Units of Dry Measure

For dry measure, or dry capacity, the basic unit is the bushel, which is divided into 4 pecks, 32 dry quarts, or 64 dry pints. The U.S. bushel, or Winchester bushel, is 2,150.42 cu in. and is about 3% smaller than the British imperial bushel of 2,219.36 cu in., with a similar difference existing between U.S. and British subdivisions. The barrel is a unit for measuring the capacity of larger quantities and has various legal definitions depending on the quantity being measured, the most common value being 105 dry quarts.

Differences between American and British Systems

Many American units of weights and measures are based on units in use in Great Britain before 1824, when the British Imperial System was established. Since the Mendenhall Order of 1893, the U.S. yard and pound and all other units derived from them have been defined in terms of the metric units of length and mass, the meter and the kilogram; thus, there was no longer any direct relationship between American units and British units of the same name. In 1959 an international agreement was reached among English-speaking nations to use the same metric equivalents for the yard and pound for purposes of science and technology; these values are 1 yd=0.9144 meter (m) and 1 lb=0.45359237 kilogram (kg). In the United States, the older definition of the yard as 3,600/3,937 m has continued to be used in many instances for surveying, the corresponding foot (1,200/3,937 m) being known as the survey foot; the survey foot will become obsolete in 2023.

The English units of measurement have many drawbacks: the complexity of converting from one unit to another, the differences between American and British units, the use of the same name for different units (e.g., ounce for both weight and liquid capacity, quart and pint for both liquid and dry capacity), and the existence of three different systems of weights (avoirdupois, troy, and apothecaries'). Because of these disadvantages and because of the wide use of the much simpler metric system in most other parts of the world, there have been proposals to do away with the U.S. Customary System and replace it with the metric system.

Bibliography

See L. J. Chisholm, Units of Weights and Measure: International and U.S. Customary (U.S. National Bureau of Standards, 1967).

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barrel

[′bar·əl]
(design engineering)
A container having a circular lateral cross section that is largest in the middle, and ends that are flat; often made of staves held together by hoops.
A piece of small pipe inserted in the end of a cartridge to carry the squib to the powder.
That portion of a pipe having a constant bore and wall thickness.
(mechanics)
Abbreviated bbl.
The unit of liquid volume equal to 31.5 gallons (approximately 119 liters).
The unit of liquid volume for petroleum equal to 42 gallons (approximately 158 liters).
The unit of dry volume equal to 105 quarts (approximately 116 liters).
A unit of weight that varies in size according to the commodity being weighed.
(naval architecture)
The central part of a windlass or capstan about which the cable is wound.
(optics)
A tapering cylindrical housing which contains the lenses of a camera and the iris diaphragm.
(ordnance)
The cylindrical metallic part of a gun which controls the initial direction of a projectile.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

barrel

1. A weight measure for portland cement in the US, corresponding to 376 pounds net; this measure is now obsolete.
2. (US) A vessel which holds 311/2 gal of liquid.
3. That portion of a pipe having a constant bore and wall thickness.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

barrel

1. a unit of capacity used in brewing, equal to 36 Imperial gallons
2. a unit of capacity used in the oil and other industries, normally equal to 42 US gallons or 35 Imperial gallons
3. the trunk of a four-legged animal
4. the quill of a feather
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005