Pound (international avoirdupois)

The pound avoirdupois is currently the unit of mass and weight normally used (except for precious metals and pharmaceuticals) in the United States, and traditionally has been as well in the United Kingdom and most countries of the Commonwealth of Nations.

In the 1950s, the United States entered into an international agreement that unified length and mass/weight units in the United States and Commonwealth of Nations. A single yard and pound became the official units of that name under this agreement, coming into force in the United States on July 1, 1959 and in the United Kingdom in 1963. The value of the pound, defined as 0.45359237 kg, can be designated the International avoirdupois pound as a mass unit. Prior to this international agreement, slightly different standard pounds had existed in the U. S. and U. K.

However, the pound is also used as a unit of weight, defined as equal to the force with which the Earth attracts a one-pound mass (at some standard point on the Earth's surface). When it is desired to distinguish the two, one refers to the pound-mass and the pound-force.