Topic summary
Pound (mass)
The pound or pound-mass is a unit of mass used in both the British imperial and United States customarysystems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb; an alternative symbol (when there might otherwise be a risk of confusion with the pound-force) is lbm (for most pound definitions), # (chiefly in the U.S.), and ℔ or ″̶ (specifically for the apothecaries' pound).
The unit is descended from the Roman libra (hence the symbol lb, descended from the scribal abbreviation, ℔). The English word pound comes from the Roman libra pondo ('the weight measured in libra'), and is cognate with, among others, GermanPfund, Dutchpond, and Swedishpund. These units remain in common use in many territories especially those which have not fully adopted the metric system.
Usage of the unqualified term pound reflects the historical conflation of mass and weight. This accounts for the modern distinguishing terms pound-mass and pound-force.