Calculate muzzle energy, power factor, and Taylor KO factor from bullet weight, velocity, and caliber in multiple units for game use.
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Muzzle Energy Formula
E = 1/2 * m * v^2
- E = kinetic energy at the muzzle (joules, then converted to ft·lbf)
- m = bullet mass (kilograms)
- v = muzzle velocity (meters per second)
The calculator converts your inputs to SI units, computes joules, then divides by 1.3558 to display ft·lbf. To get ft·lbf directly from grains and fps, the equivalent shortcut is E = (grains × fps²) ÷ 450,437.
The other two modes use these formulas:
PF = (grains * fps) / 1000
TKO = (grains * fps * caliber_in) / 7000
Power Factor and Taylor KO require imperial units by definition. The calculator handles the conversion if you enter metric values. All results assume muzzle conditions (point of exit from the barrel) and ignore drag.
Reference Tables
Typical muzzle energy ranges for common cartridges:
| Cartridge | Bullet | Velocity | Energy |
|---|---|---|---|
| .22 LR | 40 gr | 1080 fps | ~104 ft·lbf |
| 9mm Luger | 124 gr | 1150 fps | ~364 ft·lbf |
| .45 ACP | 230 gr | 850 fps | ~369 ft·lbf |
| .223 Rem | 55 gr | 3240 fps | ~1282 ft·lbf |
| .308 Win | 150 gr | 2820 fps | ~2648 ft·lbf |
| .30-06 | 180 gr | 2700 fps | ~2913 ft·lbf |
| .300 Win Mag | 180 gr | 2960 fps | ~3502 ft·lbf |
| .375 H&H | 300 gr | 2530 fps | ~4263 ft·lbf |
| .458 Win Mag | 500 gr | 2090 fps | ~4849 ft·lbf |
Common energy guidelines for ethical hunting (impact energy, not muzzle):
| Game | Suggested Minimum Energy |
|---|---|
| Varmints / small game | 50–200 ft·lbf |
| Coyote, javelina | ~500 ft·lbf |
| Deer, antelope | ~1000 ft·lbf |
| Elk, black bear | ~1500 ft·lbf |
| Moose, large bear | ~2000 ft·lbf |
| Dangerous game (cape buffalo, etc.) | ~4000 ft·lbf |
Worked Example
A 150-grain .308 bullet leaves the muzzle at 2820 fps.
- Convert mass: 150 gr × 0.0000648 = 0.00972 kg
- Convert velocity: 2820 fps × 0.3048 = 859.5 m/s
- Apply formula: E = 0.5 × 0.00972 × 859.5² = 3590 J
- Convert to ft·lbf: 3590 ÷ 1.3558 ≈ 2648 ft·lbf
Why velocity matters more than weight: energy scales with the square of velocity but only linearly with mass. Doubling velocity quadruples energy. Doubling bullet weight only doubles it.
Muzzle vs. impact energy: the calculator gives energy at the muzzle. Bullets shed velocity to drag, so impact energy at 200+ yards is meaningfully lower. Use a ballistic calculator with BC and range for downrange figures.
