Enter your projectile's weight in grains and velocity in feet per second (FPS) to calculate foot-pounds of energy (FPE) — the standard measure of kinetic energy for bullets, pellets, and arrows. The FPE Calculator also converts your result to Joules, so you can compare across measurement systems. Works for air guns, rifles, pistols, and archery.
Foot-Pounds of Energy (FPE)
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Energy in Joules
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Power Category
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A foot-pound of energy (FPE) is a unit of kinetic energy in the imperial system. It represents the energy required to move a one-pound object a distance of one foot. In ballistics, FPE is used to measure the energy a projectile carries at the muzzle or at a given range.
The FPE formula is: FPE = (Weight in grains × Velocity²) ÷ 450,240. You multiply the projectile's weight in grains by the square of its velocity in feet per second, then divide by the constant 450,240. This calculator does that math for you automatically.
The constant 450,240 is a unit-conversion factor that accounts for the difference between grains and pounds, and between feet per second and the standard units used in the kinetic energy formula (½mv²). It allows you to plug in grains and FPS directly and get FPE as the result.
A typical .45 ACP round fires a 230-grain bullet at around 830 FPS, producing approximately 352 FPE at the muzzle. This makes it a powerful defensive cartridge, though actual energy varies by load and barrel length.
Air guns producing over 12 FPE are generally considered suitable for small game hunting, while those above 30 FPE can take medium-sized game. Many jurisdictions regulate air guns above certain FPE thresholds. An air gun producing 50 FPE or more is considered highly powerful and is potentially lethal to humans.
Entry-level air pistols typically produce 1–5 FPE, while mid-range air rifles range from 10–25 FPE. High-powered PCP (pre-charged pneumatic) air rifles can produce 50–100+ FPE, making them suitable for small to medium game hunting.
To convert foot-pounds of energy to Joules, multiply FPE by 1.35582. For example, 100 FPE equals approximately 135.58 Joules. The Joule is the SI (metric) unit of energy, commonly used outside the United States.
Yes. FPE at the muzzle is the maximum; it decreases as the projectile travels downrange due to air resistance slowing the projectile's velocity. Since FPE depends on the square of velocity, even small drops in speed significantly reduce the energy at the target.