Pound (force)

Unit systemEnglish Engineering units, British Gravitational System
Unit conversions
1 lbf in ...... is equal to ...
   SI units   4.448222 N
   CGS units   444,822.2 dyn
   Absolute English System   32.17405 pdl

The pound-force (symbol: lbf[1], sometimes lbf,[2]) is a unit of force or weight used in some systems of measurement including English Engineering units and the British Gravitational System.[3] Pound force should not be confused with foot-pound, a unit of energy, or pound-foot, a unit of torque, and may be written as "lbf⋅ft". They should not be confused with pound-mass (symbol: lb), often simply called pound, which is a unit of mass.


The pound-force is equal to the gravitational force exerted on a mass of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected.[4]

The 20th century, however, brought the need for a more precise definition. A standardized value for acceleration due to gravity was therefore needed.

Product of avoirdupois pound and standard gravity

The pound-force is the product of one avoirdupois pound (exactly 0.45359237 kg) and the standard acceleration due to gravity, 9.80665 m/s2 (about 32.174049 ft/s2).[5][6][7]

The standard values of acceleration of the standard gravitational field (gn) and the international avoirdupois pound (lb) result in a pound-force equal to 4.4482216152605 N:[8]

This definition can be rephrased in terms of the slug. A slug has a mass of 32.174049 lb. A pound-force is the amount of force required to accelerate a slug at a rate of 1 ft/s2, so:

Other Languages
Deutsch: Pound-force
فارسی: پوند-نیرو
français: Livre-force
한국어: 파운드힘
italiano: Libbra forza
עברית: ליברת-כוח
македонски: Фунта-сила
日本語: 重量ポンド
norsk nynorsk: Poundforce
polski: Funt-siła
português: Libra (força)
Simple English: Pound-force
中文: 磅力