Pound-force (lbf) is the standard imperial unit of force in the United States, defined as the gravitational force exerted on one pound of mass at sea level. It appears in bolt tension ratings, material testing, and mechanical engineering specifications throughout North America. One pound-force equals approximately 4.448 newtons.

Ounce-force (ozf) equals approximately 0.278 newtons, the imperial unit for small force measurements in precision engineering, spring calibration, and micro-mechanical testing. It is particularly useful for measuring trigger pull weights, small spring tensions, and delicate instrument calibrations. One ounce-force equals about 1/16 of a pound-force.