Pound-force (lbf) is a unit of force in the Imperial and U.S. customary systems. It is defined as the force exerted by gravity on a mass of one pound at standard gravity (9.80665 m/s²). Thus, 1 lbf = 4.44822 N.
The concept of pound-force emerged in the 19th century as engineers and scientists required a consistent unit of force. The Imperial system formalized it, aligning with the use of pounds as a unit of mass. The establishment of the gravitational constant in the late 19th century further solidified its application.
Pound-force is widely used in engineering, especially in the United States, for measuring forces in mechanical and civil engineering. It is also common in automotive specifications and aerospace applications.