About this tool
The Arrow FOC Calculator is a free, in-browser tool for archers and bowhunters that measures an arrow's front-of-center (FOC) — the share of its total length that sits ahead of the physical balance point. FOC governs how stably an arrow flies and how well it holds a line downrange, so tuners adjust point weight, inserts and shaft length to hit a target FOC. Everything is calculated locally as you type.
The balance point is where the finished arrow balances on a straight edge, measured from the nock throat (the base of the arrow). The formula is FOC% = ((balancePoint − arrowLength ÷ 2) ÷ arrowLength) × 100. For example, a 29-inch arrow that balances at 19 inches has a center at 14.5 inches, so FOC = ((19 − 14.5) ÷ 29) × 100 = 15.5%. If you also enter total arrow weight in grains and speed in feet per second, the tool adds kinetic energy KE = grains × fps² ÷ 450240 (ft·lb) and momentum = grains × fps ÷ 225218.
Common FOC guidance: target and field archery sit around 7-10%, general hunting arrows around 10-15%, high-FOC setups 15-19%, and extreme-FOC (EFOC) builds above 19% for deep penetration. Higher FOC improves forgiveness and penetration but can drop trajectory, so most hunters balance it against speed.
Frequently asked questions
How do I find the balance point?
Lay the fully built arrow — point, insert, nock and fletching installed — across a thin edge and slide it until it balances level. Measure from the nock throat (the deepest part of the nock groove) to that balance point in inches. That distance is the balance point the calculator asks for.
What FOC should a hunting arrow have?
There is no single right answer, but most hunting setups land between 10% and 15%. Many penetration-focused shooters push to 15-19% (high FOC) or above 19% (extreme FOC) by adding point and insert weight. Target archers usually prefer 7-12% for a flatter trajectory.
Does higher FOC always fly better?
Not always. More front weight improves stability and penetration and helps broadheads steer true, but it also lowers arrow speed and drops the trajectory faster, so you aim higher at distance. The best FOC balances forgiveness against the flatness you need for your ranges.
How is kinetic energy calculated?
If you enter total arrow weight in grains and measured speed in feet per second, KE = weight × speed² ÷ 450240 gives foot-pounds, and momentum = weight × speed ÷ 225218. Both help compare arrow lethality; many hunters want at least 25-40 ft·lb depending on the game.
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