# Bullet Energy Calculator

Calculate bullet muzzle energy in ft-lbs and Joules. Enter bullet weight and velocity to find kinetic energy, Taylor KO Factor, and USPSA power factor.

## What this calculates

Muzzle energy measures the kinetic energy of a bullet as it leaves the barrel. A 147-grain 9mm bullet at 990 fps produces about 320 ft-lbs of energy, while a 230-grain .45 ACP at 830 fps produces about 352 ft-lbs. This calculator also computes the Taylor Knockout Factor, which accounts for bullet diameter as a rough stopping power comparison.

## Inputs

- **Bullet Weight** (gr) — min 1 — Bullet weight in grains (1 grain = 0.0648 grams).
- **Muzzle Velocity** (fps) — min 0 — Bullet velocity in feet per second.
- **Bullet Diameter** (in) — min 0.1 — Bullet diameter for Taylor KO Factor (e.g., 0.355 for 9mm, 0.452 for .45 ACP).

## Outputs

- **Muzzle Energy** (ft-lbs) — Kinetic energy in foot-pounds.
- **Muzzle Energy** (J) — Kinetic energy in Joules.
- **Taylor KO Factor** — Taylor Knockout Factor (higher = more stopping power).
- **Power Factor** — IPSC/USPSA power factor (weight in grains * velocity / 1000).

## Details

The muzzle energy formula in imperial units is:

KE = (bullet weight in grains * velocity in fps2) / 450,240

The constant 450,240 comes from 2 * 7,000 (grains per pound) * 32.174 (gravitational acceleration in ft/s2). This gives the result in foot-pounds.

**Taylor Knockout Factor:**
TKO = (weight in grains * velocity in fps * bullet diameter in inches) / 7,000

Developed by big game hunter John "Pondoro" Taylor, TKO accounts for bullet diameter as a factor in stopping power. For comparison:

  - 9mm (147gr @ 990fps): ~320 ft-lbs, TKO ~7.4

  - .45 ACP (230gr @ 830fps): ~352 ft-lbs, TKO ~12.3

  - .308 Win (168gr @ 2,650fps): ~2,620 ft-lbs, TKO ~19.3

  - .375 H&H (300gr @ 2,530fps): ~4,263 ft-lbs, TKO ~40.5

**Power Factor:**
Competition shooters use power factor (bullet weight * velocity / 1,000) to classify loads. USPSA Major is 165+, Minor is 125+.

## Frequently Asked Questions

**Q: How is muzzle energy calculated?**

A: Muzzle energy uses the kinetic energy formula KE = 1/2 mv^2, adapted for ballistic units. In imperial: KE (ft-lbs) = (bullet weight in grains * velocity in fps squared) / 450,240. The constant converts grains to pounds and accounts for gravitational acceleration.

**Q: What is a good muzzle energy for self-defense?**

A: Most defensive handgun loads produce between 300 and 500 ft-lbs. The FBI standard for defensive ammunition performance is based on penetration depth (12-18 inches in ballistic gelatin), not just energy. Energy alone does not determine stopping effectiveness.

**Q: What is the Taylor Knockout Factor?**

A: The Taylor KO Factor was developed by big game hunter John Taylor to compare the stopping power of different cartridges for dangerous game. It multiplies weight, velocity, and bullet diameter, giving more credit to larger-diameter bullets. Anything above 40 is considered suitable for dangerous African game.

**Q: Does higher muzzle energy mean more recoil?**

A: Not directly. Recoil depends on the momentum of the bullet and powder gases, the weight of the firearm, and the action type. A heavy bullet at moderate speed and a light bullet at high speed can have the same energy but very different recoil characteristics.

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Source: https://vastcalc.com/calculators/physics/bullet-energy
Category: Physics
Last updated: 2026-04-08