What is the kinetic energy formula for a crossbow bolt?

Kinetic energy in foot-pounds equals bolt weight in grains times velocity in fps squared, divided by 450,240. The constant folds in the 7,000 grains per pound conversion and the gravitational factor, giving energy directly in ft-lbs.

How much kinetic energy do I need to hunt deer?

Most archery guidelines call for at least 25 to 41 ft-lbs for deer-sized game. Modern crossbows easily exceed this, often producing 90 to 130 ft-lbs, so energy is rarely the limiting factor — shot placement and broadhead choice matter more.

What is momentum and why does it matter?

Momentum is mass times velocity and, expressed in slug-fps, is a strong predictor of penetration. A heavier, slower bolt can carry more momentum than a light, fast one at the same energy, which is why many bowhunters favour heavier arrows for deep penetration on large game.

Should I include the broadhead weight?

Yes. Always weigh the complete arrow you will actually shoot, including the broadhead or point, insert, wraps, and nock. The broadhead alone is typically 100 to 150 grains and significantly affects total energy and momentum.

Does higher energy guarantee an ethical kill?

No. Energy is only one factor. A well-placed shot with a sharp, properly tuned broadhead at an appropriate range is far more important. Excess energy cannot compensate for poor placement, and most jurisdictions also set minimum equipment requirements you must meet.

Crossbow Kinetic Energy Calculator

The crossbow kinetic energy calculator tells you how much striking energy your bolt delivers, a key figure for choosing the right game to hunt and for tuning your setup for clean, ethical harvests.

How it works

Kinetic energy is computed directly in foot-pounds from the complete bolt weight and its speed:

KE (ft-lbs) = (weight_grains × speed_fps²) / 450240

The constant 450240 combines the 7,000 grains-per-pound conversion with twice the gravitational constant, so the result comes out in ft-lbs. The tool also reports momentum in slug-fps using weight × speed / 225218, because momentum predicts penetration better than energy alone — a heavy bolt punches deeper than a light one of equal energy.

Energy guidelines and notes

The result is matched against widely cited archery energy tiers: under 25 ft-lbs for small game, 25 to 41 for deer and similar, 42 to 65 for elk and bear, and 65-plus for the largest game. A typical 400-grain bolt at 370 fps produces about 121 ft-lbs — comfortably in the large-game band. Remember that these numbers are general references: a razor-sharp, well-tuned broadhead and correct shot placement matter as much as raw energy, and your local regulations may set minimum draw weight or arrow requirements you must meet.