What is foot-pounds of energy?
Foot-pounds (ft-lb) is a unit of energy commonly used to describe the kinetic energy of a moving projectile, such as a bullet or arrow, at a given point in its flight.
The formula
Using weight measured in grains (a small mass unit common in ammunition), kinetic energy in foot-pounds is calculated as KE = (Weight × Velocity2) ÷ 450,240, where velocity is in feet per second. The constant 450,240 combines the grains-to-slugs mass conversion with the factor of one-half from the standard KE = ½mv2 formula.
This is muzzle or point-of-impact energy based on a single velocity measurement; actual energy delivered on impact also depends on projectile design, angle, and what it strikes. This calculator is for general reference and educational purposes.
Last reviewed August 2026