Foot-Pounds of Energy Calculator
Kinetic energy in foot-pounds from mass and velocity — the unit used for muzzle energy, torque work and imperial mechanics.
Kinetic energy in imperial units.
How the foot-pounds of energy calculator works
A foot-pound is the work done lifting one pound through one foot — 1.3558 joules. Muzzle energy is conventionally quoted in it, computed from grains and feet per second.
The standard ballistic shortcut, E = mv²/450,240, folds the conversions into one constant — but that constant is a legacy approximation built on g = 32.16 ft/s². This page uses the exact SI definitions instead (1 grain = 64.79891 mg, 1 ft·lb = 1.3558179483 J), so it reads about 0.05% below the traditional formula. The exact figure is the correct one.
Formula: E(ft·lb) = m(gr) × v(fps)² / 450,240
Worked examples
| Inputs | Energy | Note |
|---|---|---|
| 150 gr at 2,800 fps | 2,610.8 ft·lb | 2,611 ft·lb — a .308 rifle load |
| 230 gr at 850 fps | 368.92 ft·lb | 369 ft·lb — a .45 ACP |
| Metric input | 2,602.79 ft·lb | the same rifle load in SI |
FAQFrequently asked questions
What is a foot-pound?
The work done lifting one pound one foot — 1.3558 joules. Note it is a unit of energy, not the pound-foot of torque.
What is the 450,240 formula?
E = mv²/450,240 with mass in grains and velocity in fps. The constant is 2 × 7,000 × 32.16, so it bakes in an old value of g and runs about 0.05% high. This page uses the exact SI conversions instead, which is why it reads a pound or two lower on a rifle load.
How many grains in a pound?
7,000 exactly.
Is muzzle energy a good measure of effect?
Only partly. Momentum, bullet construction and where it lands matter at least as much, which is why the figure is often over-read.
Why does velocity matter more than mass?
Because energy scales with the square of velocity and only linearly with mass — the same reason it matters in every other collision.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Physical Laboratory — the UK's national measurement institute
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.