What is a Foot-Pound per Second?

The foot-pound per second (ft·lb/s) is the American mechanical-power unit, used in engineering and machine-rating contexts. James Watt's original definition of 1 horsepower was 33,000 ft·lb/min = 550 ft·lb/s, so the foot-pound per second is the granular American power unit underlying horsepower calculations. It is rare in everyday use (kW or hp dominate American power specifications) but appears in engineering thermodynamics textbooks, mechanical-design calculations, and ballistics-energy contexts. The ft·lb/s relates to the watt (1 ft·lb/s ≈ 1.356 W), horsepower (550 ft·lb/s = 1 hp), and the BTU per hour (1 ft·lb/s ≈ 4.626 BTU/h). It is part of the legacy US customary unit system that retains a foothold in mechanical engineering despite metric advancement.

Visual reference for how the foot-pound per second relates to other power units. Each row links to the full converter for that pair.

• Older US mechanical-engineering calculations
• Some US physics textbooks
• Classical-mechanics problems

• ✓1 ft·lbf/s = 1.356 W.
• ✓550 ft·lbf/s = 1 mechanical hp.
• ✓Rarely needed today outside archival references.

• ✗Confusing ft·lbf/s (power) with ft·lbf (torque or work).
• ✗Using in modern specifications — prefer W or kW.
• ✗Mixing with foot-pound (energy) in same calculation.