Pound (mass)
The pound or pound-mass (abbreviations: lb, lbm, lbm for most pounds, and ℔ or ″̶ specifically for the Apothecaries' pound) is a unit of mass used in the imperial, United States customary and other systems of measurement. A number of different definitions have been used, the most common today being the international avoirdupois pound which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb.
The unit is descended from the Roman libra (hence the abbreviation "lb"). The English word pound is cognate with, among others, German Pfund, Dutch pond, and Swedish pund. All ultimately derive from a borrowing into Proto-Germanic of the Latin expression lībra pondō ("a pound by weight"), in which the word pondō is the ablative case of the Latin noun pondus ("weight").
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.
The United States and countries of the Commonwealth of Nations agreed upon common definitions for the pound and the yard. Since 1 July 1959, the international avoirdupois pound (symbol lb) has been defined as exactly 0.45359237 kg.
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