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Arrow FOC Calculator — Front of Center for Archery

Calculate arrow Front of Center (FOC%) from length and balance point, or from individual components. Ratings for target, hunting, and extreme FOC applications.

Total arrow length, nock throat to tip

Distance from nock throat to balance point

FOC — Low / Target

7.1%

Acceptable for indoor target at close range.

Formula: FOC% = (balance point from nock − arrow length / 2) / arrow length × 100
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How to Use This Calculator

  1. 1

    Measure arrow length (L)

    Measure from the nock throat (the groove holding the bowstring) to the end of the arrow shaft. Do not include the point/broadhead — measure to the shaft end only. Use inches or centimeters consistently.

  2. 2

    Find the balance point (A)

    Balance the complete arrow (with point, nock, and vanes installed) on your finger or a pen. Mark where it balances. Measure from the nock throat to that mark. This is A — the balance point distance from the nock.

  3. 3

    Calculate FOC (Simple mode)

    Enter L and A into the Simple mode. FOC% = (A − L/2) / L × 100. The calculator shows your result with a rating (Too Low / Target / Good / High FOC / Extreme FOC).

  4. 4

    Use Component mode to optimize

    If you want to adjust FOC, use Component mode. Enter arrow length, shaft weight (grains per inch from manufacturer spec), then point weight, insert weight, nock weight, and vane weight with their positions. See how changing component weights shifts your FOC.

What Each Value Means

FOC (Front of Center) (% of arrow weight)
Percentage of arrow total weight that is forward of the geometric midpoint. FOC% = (balance_point_from_nock − arrow_length/2) / arrow_length × 100. A positive FOC means more weight in the front half. Zero FOC means perfectly balanced. Negative FOC (more weight in the rear) produces extremely poor flight.
Grains per Inch (GPI) (grains per inch)
The weight of the arrow shaft per inch of length, measured in grains (1 grain = 0.0648 grams). A carbon shaft rated at 8.5 GPI and cut to 28 inches weighs 238 grains. GPI is listed in shaft manufacturer specifications. Higher GPI = heavier arrow = more penetration but slower speed.

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Frequently Asked Questions

What is FOC in archery and why does it matter?
FOC (Front of Center) is the percentage of an arrow's total weight that is forward of the arrow's geometric center. A higher FOC means more weight near the tip, which creates a more stable flight path (the heavy tip resists vane fishtailing and stabilizes at longer distances), better penetration on game, and more consistent accuracy. An arrow with too little FOC spirals or fishtails; an arrow with too much FOC can plane erratically at long range.
What is a good FOC percentage for bowhunting?
For bowhunting, most arrow manufacturers and archery experts recommend 12–15% FOC as the standard range, and 15–19% for deeper penetration on large game. Some hunters targeting maximum penetration on thick-skinned animals deliberately build 20–30%+ 'extreme FOC' setups with very heavy broadheads (200+ grains) or stacked weight systems. Standard target archery typically uses 10–15% FOC. Below 7% produces unstable flight.
How do you measure the balance point of an arrow?
Balance your arrow horizontally on your finger or a narrow edge. Slide your finger forward or backward until the arrow balances perfectly (doesn't tip). Mark that point. Measure the distance from the nock throat (the groove that holds the string) to the balance point — this is your balance point distance. Then use the FOC formula: FOC% = (balance point − arrow length/2) / arrow length × 100.
How do I increase my arrow's FOC?
To increase FOC: use a heavier point (100 → 125 → 150 → 200+ grain broadhead or field point), add a heavier insert or brass insert instead of aluminum, add collar or weight screws at the front of the shaft, or use a lighter nock and lighter vanes. To decrease FOC: use a lighter point, heavier nock, heavier vanes, or rear wraps.
What is the AMO/ATA FOC formula?
The official Archery Trade Association (ATA) formula for FOC: FOC% = (A − L/2) / L × 100. Where A is the distance from the nock throat to the balance point (in the same units as L), and L is the total arrow length from nock throat to tip of arrow shaft (not including the point). Both A and L must be in the same units (inches or centimeters).