FOC Calculator (Arrow Front of Center)
Free FOC calculator for arrows. Work out front of center from your arrow length and balance point, or estimate it from component weights, and see total arrow weight and grains per pound.
Work out your arrow's front of center two ways: from a measured balance point, or estimated from your component weights. The build mode also reports total arrow weight and grains per pound of draw weight.
Measurements
Measure from the throat of the nock to the end of the shaft (do not include the point), then balance the finished arrow on a straight edge.
Nock throat to end of shaft
Where the complete arrow balances
Normal FOC — The range most factory arrows land in. A good all-round balance of trajectory and stability.
How this was calculated
What the number means
| FOC range | Description |
|---|---|
| under 7% | Low FOC — Flatter trajectory but less forgiving in flight. Common on target setups shooting light points. |
| 7–10% | Normal FOC — The range most factory arrows land in. A good all-round balance of trajectory and stability. |
| 10–15% | High FOC — Popular for hunting: better arrow flight stability and forgiveness, with only a modest drop in trajectory. |
| 15–19% | Extreme FOC — Ashby-style setup. Strong penetration and stability; expect a noticeably more arcing trajectory past 30 yards. |
| 19%+ | Ultra-extreme FOC — Maximum penetration territory. Trajectory drops off quickly, and arrow tuning gets fussy. |
How to calculate arrow FOC
- 1
Measure the arrow length
From the throat of the nock — where the string sits — to the end of the shaft. Do not include the point or broadhead.
- 2
Find the balance point
With the arrow fully built, balance it on a straight edge and mark the spot.
- 3
Measure to the balance point
Measure from the nock throat to the mark. Call this A.
- 4
Apply the formula
FOC% = 100 × (A − L ÷ 2) ÷ L. The calculator does this and tells you which band the result falls into.
The AMO formula, step by step
FOC% = 100 × (A − L ÷ 2) ÷ L
L is the arrow length, measured from the throat of the nock to the end of the shaft. Points and broadheads are deliberately excluded — this is a measure of the shaft, not the whole assembly.
A is the distance from the nock throat to the balance point of the finished arrow, with everything fitted.
L ÷ 2 is the physical centre of the arrow, so A − L ÷ 2 is how many inches forward of centre the balance point sits. Dividing by L and multiplying by 100 expresses that as a percentage of the arrow's length, which is what makes the number comparable between arrows of different lengths.
FOC by arrow build
Changing your FOC
To raise FOC
- Heavier point or broadhead — the single biggest lever
- Brass or steel insert instead of aluminium
- Add an outsert or collar behind the point
- Shorter shaft, if your draw length allows
- Smaller vanes and a lighter nock
- Skip the wrap
To lower FOC
- Lighter field point or broadhead
- Aluminium insert instead of brass
- Longer shaft
- Larger vanes or feathers, or a wrap
- Add a lighted or heavier nock
Remember that adding point weight makes a shaft act weaker in the bow. A big jump in FOC usually calls for a stiffer spine, so re-check your tune after any significant change.
Frequently asked questions
What is FOC in archery? ▾
FOC stands for front of center: the percentage of the arrow's length by which its balance point sits ahead of the true middle. A higher FOC means more of the arrow's weight is concentrated at the point end.
What is the FOC formula? ▾
FOC% = 100 × (A − L ÷ 2) ÷ L, where L is the arrow length measured from the throat of the nock to the end of the shaft (not including the point) and A is the distance from the nock throat to the balance point of the complete arrow.
What is a good FOC percentage? ▾
Roughly 7–10% is normal and typical of factory arrows. Hunters often aim for 10–15% for better flight stability and penetration. Anything from 15–19% is called extreme FOC, and above 19% is ultra-extreme — great penetration, but a noticeably arcing trajectory.
How do I measure my arrow's balance point? ▾
Build the arrow completely — point, insert, nock and fletching all fitted — then rest it across a straight edge and slide it until it balances. Mark that spot and measure back to the throat of the nock.
Does higher FOC mean better penetration? ▾
Up to a point. More weight forward makes the arrow more stable in flight and helps it drive straight into the target, which is why Ashby-style setups push FOC high. Past that, the trajectory drops off steeply and tuning becomes fussier, so most hunters settle in the 12–19% range.
How do I increase my arrow's FOC? ▾
Add weight to the front (a heavier point, a brass insert, or an outsert), take weight off the back (smaller vanes, a lighter nock, no wrap), or shorten the shaft — a shorter arrow raises FOC for the same point weight.
Does FOC change the arrow's spine? ▾
Effectively yes. Adding point weight makes a shaft behave weaker (more flexible) in the bow, so a heavy-FOC build usually needs a stiffer shaft than the same setup with a light point.
About this Calculator
Free FOC calculator for arrows. Work out front of center from your arrow length and balance point, or estimate it from component weights, and see total arrow weight and grains per pound.