Bullet Energy Calculator
This bullet energy calculator works out the kinetic energy a projectile carries from just two numbers: its weight in grains and its velocity in feet per second. Kinetic energy is the standard way shooters and hunters compare loads, because it captures how much work a bullet can do when it strikes. The calculator uses the well-established ballistics formula, energy in foot-pounds equals bullet weight in grains times velocity squared, divided by the industry constant 450,240, then converts the result into joules for those who prefer metric units. It also reports the velocity in metres per second and the bullet's momentum, so you can see the full picture at the muzzle, or at any range if you enter a downrange velocity from your ballistic app or chronograph. Hunters in New Zealand use energy figures to check that a load meets the rough minimums often quoted for deer, tahr and larger game, while target shooters use them to compare handloads. Enter the grain weight printed on your ammunition box and the muzzle velocity from the maker or your chronograph, and the numbers update as you type. Remember that energy is only one part of terminal performance: bullet construction, expansion, sectional density and shot placement all matter, so treat the figure as a comparison, not the whole story.
A 150 gr bullet at 2,820 fps carries 2,649 ft·lb (3,592 J) of kinetic energy at the muzzle.
Energy uses the standard ballistics formula with the constant 450,240. Enter a downrange velocity to see energy at range. Estimate for comparison only; terminal performance also depends on the bullet.
How it works
Kinetic energy in foot-pounds equals the bullet weight in grains times the velocity in feet per second squared, divided by 450,240. That constant folds in the 7,000 grains per pound and the acceleration of gravity, so you can work in the familiar grain and fps units. Multiplying the foot-pound answer by 1.3558 gives joules. Velocity in metres per second is the fps figure times 0.3048, and momentum is the bullet mass in kilograms times that velocity.
Worked example
Take a 150 grain bullet leaving the muzzle at 2,820 fps, a typical .308 Winchester load. Energy is (150 x 2,820 x 2,820) / 450,240, which is about 2,649 foot-pounds. Multiplying by 1.3558 gives 3,592 joules. The velocity is 2,820 x 0.3048, or about 860 metres per second, and the momentum is roughly 8.4 kilogram metres per second. Drop the velocity to a downrange 2,300 fps and the energy falls to about 1,762 foot-pounds, showing how quickly energy bleeds off with range.
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