Foot-pound (ft·lb)

The work performed in raising a weight of one pound through a vertical distance of one foot.

The foot-pound gave British engineers a direct and physically intuitive measure of mechanical work, which is why James Watt expressed horsepower in foot-pounds per minute rather than in any abstract unit. It endures in two specialised corners of modern life: the torque figures quoted for engines and fastenings, and the muzzle energy of firearms and air rifles, where British law sets legal limits in foot-pounds.