Arrow FOC Calculator

Enter your finished arrow length and its balance point to find the Front of Center (FOC) percentage — the share of arrow weight ahead of the physical center.

Quick Facts

Formula
FOC% = 100 × (Balance point − Length ÷ 2) ÷ Length
Standard AMO archery method. Measure both distances from the throat of the nock on a fully built arrow.

Your Results

Calculated
FOC
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Front of Center percentage
Physical center
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Length ÷ 2, from nock throat
Balance offset
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How far ahead of center the balance point sits
Setup class
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Typical use for this FOC

Ready

Enter your arrow length and balance point, then calculate.

What FOC Means for an Arrow

FOC stands for Front of Center. It is the percentage of an arrow's total length that its balance point sits ahead of the true physical center of the shaft. A higher FOC means more of the arrow's weight is concentrated up front, toward the point; a lower FOC means the weight is spread more evenly. FOC is one of the most-cited tuning numbers in archery because it directly affects how stable an arrow flies downrange and how it behaves on impact.

The reason weight distribution matters comes down to physics: the front of the arrow leads in flight, and the fletching at the rear steers. When more mass is forward of center, the arrow acts a bit like a lawn dart — the nose stays pointed into the wind and the rear corrects quickly, which improves stability at distance. Too little front weight and the arrow can be twitchy; too much and it drops faster because the extra point mass steepens the trajectory.

The FOC Formula

The standard AMO (Archery Manufacturers Organization) method uses just two measurements, both taken on a fully built arrow (insert, point, nock, and fletching all installed):

FOC (%) = 100 × (A − L ÷ 2) ÷ L

  • L = the overall arrow length, measured from the throat of the nock (the deepest point of the nock groove where the string sits) to the end of the shaft.
  • A = the distance from that same nock throat to the arrow's balance point.
  • L ÷ 2 = the physical center of the arrow.

In plain terms: find how far the balance point is ahead of the center (that is A − L/2), then express it as a percentage of the whole arrow length. If the balance point sits exactly at center, FOC is 0%. Note that the point and insert are not weighed directly in this formula — their effect shows up automatically because they pull the balance point forward.

A worked example

Suppose an arrow is 29 inches long and balances at 16 inches from the nock throat. The center is 29 ÷ 2 = 14.5 inches. The balance point is 16 − 14.5 = 1.5 inches ahead of center. FOC = 100 × 1.5 ÷ 29 = 5.17%. Add a heavier point and the balance point moves forward to, say, 17 inches: FOC = 100 × (17 − 14.5) ÷ 29 = 8.62%.

Reference FOC Ranges

  • 7–10% — Target and 3D: Prioritizes a flat, forgiving trajectory. Most indoor and competition setups live here.
  • 10–15% — Hunting: The most common bowhunting window. Adds forward weight for better penetration and downrange stability without a big trajectory penalty.
  • 15–19% — EFOC (Extreme FOC): Popular with hunters chasing maximum penetration on large or heavy-boned game.
  • 19%+ — Ultra-EFOC: Very front-heavy. Excellent penetration but noticeably steeper arrow drop, so it demands precise range estimation.

These are guidelines, not hard rules. The "right" FOC depends on your bow, draw weight, distance, and whether you value trajectory or penetration more.

Frequently Asked Questions

What is a good FOC percentage for an arrow?
It depends on your goal. Target and 3D archers typically run 7–10% FOC for a flat, forgiving trajectory. Bowhunters usually aim for 10–15% for better penetration and stability, EFOC is about 15–19%, and ultra-EFOC is 19% and up. There is no single correct value — heavier front weight improves penetration and stability but steepens trajectory.
How do I increase or decrease my arrow's FOC?
To raise FOC, add weight toward the front: a heavier point or field tip, heavier or brass inserts, or a weighted insert/collar. To lower FOC, use a lighter point, a lighter insert, or add a small amount of weight toward the rear (heavier nock or wraps). Even a 25–50 grain change at the point end shifts FOC noticeably. Re-measure the balance point after any change.
Does higher FOC always mean better arrow flight?
No. More front weight improves stability and penetration up to a point, but it also lowers total arrow speed and steepens the trajectory, so the arrow drops faster and requires more precise range estimation. Very high FOC can also over-stress the shaft's dynamic spine. Most archers find a sweet spot in the ranges above rather than maximizing FOC.
Do I measure arrow length including the point?
The AMO length used in this formula is measured from the throat of the nock to the end of the shaft (carbon or aluminum), not to the tip of the point. Always take the balance-point measurement from the same reference — the nock throat — so both numbers use a consistent origin.

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