Bullet Energy Calculator

Enter bullet weight and velocity to compute kinetic energy in foot-pounds and joules, plus equivalent bullet mass and power factor, using the standard ballistics energy formula.

Quick Facts

Formula
KE (ft-lbs) = weight (grains) x velocity (fps)^2 / 450,240
The classical E = 1/2 m v^2, rewritten so grains and fps plug in directly and the answer comes out in foot-pounds.
Unit conversions
1 ft-lb = 1.35582 J  |  1 grain = 0.0648 g
Used to report energy in joules and weight-equivalent mass in grams.

Your Results

Calculated
Kinetic energy
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Foot-pounds (ft-lbs)
Kinetic energy
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Joules (J)
Bullet mass
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Grams (equivalent)
Power factor
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Weight x velocity / 1,000

Ready

Enter bullet weight and velocity, then press Calculate.

About the Bullet Energy Calculator

This calculator finds a bullet's kinetic energy the same way ammunition makers and ballisticians do: from its weight and velocity, using the classical kinetic energy formula rewritten for the units firearms are measured in — grains for weight and feet per second (fps) for velocity.

The formula

Kinetic energy is E = ½mv². Since bullets are weighed in grains (1 grain = 1/7,000 lb) rather than slugs, the mass-to-slug conversion is folded into a single constant so the formula can be applied directly:

  • Energy (ft-lbs) = Weight (grains) × Velocity (fps)² ÷ 450,240
  • 450,240 = 2 × 7,000 × 32.16, converting grains to slugs using standard gravitational acceleration, so the result comes out directly in foot-pounds.
  • To convert to joules, multiply foot-pounds by 1.35582 (the standard ft-lb-to-joule conversion).

Power factor

Practical shooting sports such as USPSA and IPSC use a related but simpler metric called power factor: weight (grains) × velocity (fps) ÷ 1,000. Power factor is linear in velocity, not squared like energy, so it is not a measure of energy — it exists purely to classify loads as "major" or "minor" for scoring, and is reported here for reference alongside the energy values.

Getting accurate results

  • Use the chronographed velocity for your specific load and barrel length rather than a generic box or catalog velocity — actual muzzle velocity varies with barrel length, ammunition lot, and temperature.
  • Bullet weight in grains is printed on factory ammunition boxes and bullet packaging; handloaders should use the actual weighed bullet, not the powder charge.
  • This formula computes energy at whatever velocity you enter. To estimate downrange energy, enter the velocity at that distance (from a ballistics chart or chronograph) instead of the muzzle velocity.

Frequently Asked Questions

What is the formula for bullet energy?
Bullet kinetic energy in foot-pounds is weight in grains times velocity in feet per second squared, divided by 450,240: KE = W × V² ÷ 450,240. This is the classical kinetic energy formula E = ½mv² rewritten so weight can be entered in grains and velocity in fps while the result comes out directly in foot-pounds.
How much energy does a bullet need for hunting?
Hunter education materials commonly reference roughly 1,000 ft-lbs at impact as a rule-of-thumb minimum for deer-sized game and 1,500–2,000+ ft-lbs for elk-sized game, but these are general guidelines, not laws. Effective, ethical harvests depend on shot placement and bullet construction as much as raw energy, and some jurisdictions set their own minimum caliber or energy rules, so check local hunting regulations.
What is power factor and how does it differ from energy?
Power factor (weight in grains times velocity in fps, divided by 1,000) is a linear metric used by practical shooting sports like USPSA and IPSC to classify loads as major or minor for scoring. Kinetic energy scales with velocity squared, so power factor and energy rank loads differently — a fast, light bullet can have a similar power factor to a slow, heavy one while carrying quite different energy.
Does this calculator account for barrel length or bullet expansion?
No. It computes kinetic energy directly from the velocity you enter, so it automatically reflects whatever barrel length, load, or distance produced that velocity — but it does not model bullet expansion, penetration, or other terminal-ballistics effects. Enter a downrange velocity from a chronograph or ballistics chart to estimate energy at that distance instead of at the muzzle.

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