footpounds

Footpounds, or foot-pound force (ft·lbf), is a unit of energy or work in the British engineering and US customary measurement systems. It is defined as the work performed when a force of one pound-force acts over a displacement of one foot. In practical terms, one foot-pound of work equals the energy transferred by moving a one-pound force a distance of one foot.

Because torque is also expressed in pound-foot, care is needed to distinguish energy from torque. Energy or work is usually denoted ft·lbf (or ft·lb in some contexts) whereas torque is commonly written as lb-ft. To avoid ambiguity, many technical sources use ft·lbf for energy and lb-ft for torque.

The relationship to the metric system is direct: 1 ft·lbf equals 1.3558179483314 joules, roughly 1.36 J. Conversely, 1 joule is about 0.737562149277 ft·lbf. These exact factors reflect the definitions of the pound-force and standard gravity. In practical terms, 50 ft·lbf is about 67.8 J, and 1 hp·h equals about 1,980,000 ft·lbf (roughly 2.65 MJ).

Foot-pounds have historically been used in mechanical engineering, automotive specifications, and ballistics, particularly in the United States. They appear in energy ratings, wrench torque settings described as energy, and in work calculations for engines and machines. With the global shift to SI units, ft·lbf is often replaced by joules, but the unit remains common in legacy data and certain industries.

Overall, footpounds serve as a conventional unit for expressing work and energy in systems that rely on foot and pound-force, and they are foundational for converting between imperial and metric energy measurements.