Avoirdupois weight

Avoirdupois Weight

The Avoirdupois weight system is a system of weights (or, more properly, mass) based on a pound of 16 ounces. It is the everyday system of weight used in the United States and is used for most everyday purposes in the United Kingdom. The term "avoirdupois" is derived from the Anglo-Norman French "aveir de peis" (goods of weight or property).

History

The avoirdupois system was first commonly used in the 13th century and was updated in 1959. Prior to the adoption of the international yard and pound agreement of 1959, the definitions of the pound and ounce varied slightly in different jurisdictions. The differences were, however, insignificant for most practical purposes.

Units

The basic units of the avoirdupois weight system are the pound and the ounce. The pound is defined as exactly 0.45359237 kilograms, and the ounce is defined as exactly 1/16 of a pound. In addition to the pound and ounce, the avoirdupois system also includes smaller units such as the grain and larger units such as the hundredweight and the ton.

Usage

Today, the avoirdupois system is used in the United States for all goods except precious metals, gems, and drugs. In the United Kingdom, it is used for most purposes, with the notable exception of road signs, which use metric units. The avoirdupois system is also used in Canada for some purposes, and it is the everyday system of weight in the Republic of Ireland.

See also

• Troy weight
• Apothecaries' system
• Imperial units
• United States customary units

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