Kinetic Energy & Momentum Calculator
Calculate arrow kinetic energy (ft-lbs) and momentum (slug-ft/s) from speed and arrow weight, and see which game animals your setup is suited for.
Kinetic energy
- Small game: under 25 ft-lbs
- Medium game: 25–41 ft-lbs
- Large game: 42–65 ft-lbs
- Toughest game: 65+ ft-lbs
Kinetic Energy and Momentum Formulas
Kinetic energy (KE) tells you how much work an arrow can do. Momentum tells you how hard it is to stop. The Better Outdoors calculator uses the standard archery formulas:
- Kinetic energy (ft-lbs) = arrow weight (grains) × speed (fps)² ÷ 450,240
- Momentum (slug-ft/s) = arrow weight (grains) × speed (fps) ÷ 225,218
| Game class | Typical kinetic energy guideline | Examples |
|---|---|---|
| Small game | Under 25 ft-lbs | Rabbit, turkey, coyote |
| Medium game | 25–41 ft-lbs | Whitetail, antelope |
| Large game | 42–65 ft-lbs | Elk, black bear, wild boar |
| Toughest game | 65+ ft-lbs | Grizzly, moose, cape buffalo |
Kinetic Energy vs. Momentum: Which Matters More?
Light, fast arrows score high on kinetic energy. Heavy arrows score higher on momentum, and momentum tracks penetration more closely, especially through bone on bigger animals. That is why elk and bear hunters often step up to 475–550 grain arrows even though they lose some speed. Reviewing a new bow? Compare real setups in our Bear Alaskan XT review and Mathews Lift 29.5 review.
Build a harder-hitting arrow
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Frequently Asked Questions
How much kinetic energy do I need to kill a deer with a bow?
A common guideline for whitetail is 25 to 41 ft-lbs of kinetic energy, with most modern compound setups producing well over 50 ft-lbs. Shot placement and a sharp broadhead matter most.
How do you calculate arrow kinetic energy?
Multiply arrow weight in grains by arrow speed in feet per second squared, then divide by 450,240. A 425 grain arrow at 285 fps produces about 76.7 ft-lbs.
What is good arrow momentum for elk?
Many elk hunters aim for roughly 0.5 slug-ft/s or more, typically from a 450 to 550 grain arrow, to improve penetration through heavy muscle and bone.
Is a heavier arrow better for hunting?
For bigger game, usually yes. Heavier arrows are slower but carry more momentum, are quieter and often penetrate deeper. For long-range target shooting, lighter arrows give a flatter trajectory.
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