FOC Calculator
Front-of-center tells you how far ahead of the middle your arrow's balance sits — the quiet number behind stable broadhead flight. Measure the balance point, enter it with your arrow length, done.
How FOC Is Calculated
FOC compares where the arrow balances with where its middle is, as a percentage of its length:
Both measurements run from the nock end, and the arrow must be complete — point, insert, fletching, wrap and nock all fitted — because every part shifts the balance. A balance point exactly at the middle gives 0%; hunting arrows sit forward of it, which is the whole idea: weight ahead of the middle pulls the arrow straight in flight and keeps it driving point-first on impact. Ashby's penetration work treats FOC as a first-order factor, which is why it earns its own calculator alongside the momentum calculator.
FOC Bands
| FOC | Where it belongs |
|---|---|
| Under 7% | Flat-shooting target setups; broadheads steer poorly this low |
| 7–11% | Classic hunting window — stable flight, flat trajectory |
| 12–15% | High FOC — better broadhead control and penetration |
| 16–19% | EFOC (extreme front of center) — Ashby territory |
| 20% + | Ultra EFOC — deliberate close-range heavy-game builds |
Tuning Your FOC
To raise FOC: add point weight (heavier field point or broadhead), fit a brass insert, or trim tail weight — smaller vanes, no wrap, a standard nock instead of a lighted one. Plan the parts list in the arrow weight calculator before spending money.
To lower FOC: do the reverse — lighter point, standard insert, heavier fletching or a wrap. Remember that point weight also weakens the arrow's dynamic spine: a big FOC jump may need a stiffer shaft, which the arrow spine calculator helps you sanity-check.
FOC Worked Examples
28.5″ arrow balancing at 17.25″: (17.25 − 14.25) ÷ 28.5 × 100 = 10.5% FOC — middle of the classic hunting window.
A 30″ arrow with a 200-grain point balancing at 19.5″: (19.5 − 15) ÷ 30 × 100 = 15.0% — high FOC, the deliberate heavy-arrow recipe.
A 29″ target arrow balancing at 16.25″: (16.25 − 14.5) ÷ 29 × 100 = 6.0% — low and flat-shooting, as target archers prefer.
FOC FAQs
What is a good FOC for hunting arrows?
Most hunting arrows fly best between 10% and 15% FOC: enough weight forward for stable broadhead flight and strong penetration, without the trajectory penalty of extreme builds. Target archers often run 7–11%. Ashby’s research favours the higher end for maximum penetration on tough game.
How do I measure my arrow’s balance point?
Balance the finished arrow — point, insert, fletching and all — on a knife edge or a fingertip until it sits level, and mark the spot. Measure from the throat of the nock (where the string sits) to that mark, in inches. That distance and your total arrow length are the calculator’s two inputs.
Can FOC be too high?
It can be more than you need. Past roughly 19–20% the arrow’s trajectory arcs noticeably, spine behaviour gets harder to tune, and the gains flatten. Extreme FOC is a deliberate choice for close-range, heavy-game setups — not a default to chase.
How do I increase my FOC?
Add weight at the front or remove it from the back: a heavier point or brass insert is the usual move; lighter vanes, no wrap and a standard (non-lighted) nock trim the tail. Every 25 grains added at the point of a typical hunting arrow moves FOC by roughly a percentage point — the arrow weight calculator helps you plan the build before you buy parts.
Does FOC affect arrow speed?
Only through total weight. FOC itself is a balance figure, not a weight — moving the same grains from tail to point leaves the speed estimate unchanged while shifting FOC several points. That is exactly why it is worth calculating separately: two arrows of identical weight and speed can fly very differently.
- Ashby Bowhunting Foundation — Dr Ed Ashby’s arrow penetration research — the source of the momentum and FOC guidance
- Easton Archery — shaft selection charts — the reference spine-selection and arrow-building charts this site’s groupings follow
- Gold Tip — arrow university and spine charts — manufacturer spine charts and arrow-weight data used to cross-check the tables