Enter the velocity of the bullet, the mass of the bullet, and the stopping distance into the calculator to determine the bullet impact force.
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Bullet Force Formula
The calculator uses kinetic energy as the bridge between bullet weight, velocity, force, and stopping distance. Each tab solves for a different variable using the same energy equation.
Impact force
F = (0.5 × m × v²) ÷ d
Bullet energy
E = 0.5 × m × v²
Stopping distance
d = (0.5 × m × v²) ÷ F
- F = average impact force, in newtons
- E = kinetic energy, in joules
- m = bullet mass, in kilograms
- v = bullet velocity, in meters per second
- d = stopping distance inside the target, in meters
The Impact force tab takes weight, velocity, and stopping distance and returns the average force the bullet exerts while decelerating to a stop. The Bullet energy tab returns kinetic energy and momentum from weight and velocity alone. The Stopping distance tab inverts the impact-force equation: given the energy of the bullet and an assumed average force the target can apply, it returns how deep the bullet would travel.
Reference Tables
Use these tables to sanity-check the numbers the calculator returns.
| Cartridge | Bullet weight | Velocity | Energy |
|---|---|---|---|
| .22 LR | 40 gr | 1080 ft/s | ~104 ft·lbf |
| 9mm Luger | 124 gr | 1150 ft/s | ~364 ft·lbf |
| .45 ACP | 230 gr | 850 ft/s | ~369 ft·lbf |
| .223 Rem | 55 gr | 3200 ft/s | ~1251 ft·lbf |
| .308 Win | 150 gr | 2820 ft/s | ~2649 ft·lbf |
| .338 Lapua | 250 gr | 3000 ft/s | ~4994 ft·lbf |
| Unit | Equivalent |
|---|---|
| 1 grain | 0.0648 g |
| 1 ft/s | 0.3048 m/s |
| 1 joule | 0.7376 ft·lbf |
| 1 lbf | 4.448 N |
| 1 inch | 0.0254 m |
Example and FAQ
Worked example. A 124 gr 9mm bullet leaves the muzzle at 1150 ft/s and stops after 12 inches of penetration. Convert: m = 0.00803 kg, v = 350.5 m/s, d = 0.3048 m. Energy = 0.5 × 0.00803 × 350.5² = 493 J. Average force = 493 ÷ 0.3048 = about 1,618 N, or roughly 364 lbf.
Why is this an "average" force? Real bullets do not decelerate evenly. Force spikes on initial impact and again when the bullet expands or hits dense material. The formula gives the constant force that would absorb the same total energy over the same distance.
Does this calculator account for bullet expansion or fragmentation? No. It treats the bullet as a rigid mass losing kinetic energy over a fixed stopping distance. Hollow points and fragmenting rounds transfer energy faster, so actual peak force is higher than the average shown.
Can I use this for airsoft or pellet guns? Yes. Enter the projectile weight in grams or grains and velocity in ft/s or m/s. The math is identical for any projectile, though typical pellet energies are well under 20 ft·lbf.
Why does muzzle energy differ from impact energy? A bullet loses velocity to air drag in flight. The calculator uses whatever velocity you enter, so for impact at distance you should use the velocity at the target, not at the muzzle.
