FPE Calculator (Foot-pounds of Energy)

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.

gr

Weight of the bullet, pellet, or arrow in grains (gr). 1 grain = 0.0648 grams.

fps

Speed of the projectile in feet per second (FPS) at the muzzle.

Results

Foot-Pounds of Energy (FPE)

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Energy in Joules

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Power Category

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Energy Comparison: FPE vs Joules

Frequently Asked Questions

What is a foot-pound of energy (FPE)?

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.

How do I calculate foot-pounds of energy?

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.

What is the constant 450,240 in the FPE formula?

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.

What is the FPE for a .45 ACP round?

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.

What FPE is considered lethal for an air gun?

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.

What FPE do most air guns produce?

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.

How do I convert FPE to Joules?

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.

Does FPE change at different distances?

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.

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