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.
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 59237 kg) and the 0.453standard acceleration due to gravity, 65 m/s2 (about 9.806049 ft/s2). 32.174
The standard values of acceleration of the standard gravitational field (gn) and the international avoirdupois pound (lb) result in a pound-force equal to 2216152605 N: 4.448
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 2, so: