English Units of Measurement

The principal system of a few nations, the only major industrial one being the United States. The English system actually consists of two related systems- the U.S Customary system, used in the United States and dependencies, and the British imperial.

Great Britain, the originator of the latter system, is now gradually converting to the Metric 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.

The basic unit of length is the yard (yd); the basic unit of mass (weight) is the pound (lb). Within the English units of measurement there are three different systems of weights of which the most widely used is the avoirdupois.

The troy system (named for Troyes, France, where it is said to have originated) is used only for precious metals. 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 and the scruple. For liquid measure, or liquid capacity, the basic unit is the gallon.

The U.S gallon, or wine gallon is 231 cubic inches, the British imperial gallon is the volume of 10lb of pure water at 62°F and is equal to 277.42 cu.in. The British Units of liquid capacity are thus about 20% larger than to the corresponding American units.

The U.S bushel, or Winchester bushel, is 2150.42 cu.in and is about 3% smaller than the British Imperial bushel of 2219.36 cu in.; a similar difference exists 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 substances being measured, the most common value being 105 dry quarts.