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Arrows and broadheads laid out for building and tuning

Interactive tool

Arrow FOC Calculator

Enter your finished arrow's length, balance point, and component weights to get AMO front-of-center, total grain weight, and grains per pound of draw — the three numbers that decide how an arrow flies and penetrates.

Front of center
6.9%
Low FOC — target / indoor territory
Total arrow weight
464
grains · 32% of mass up front
Grains per pound
8.4
Above the 5 gpp floor
in
in
gr
gr
gr
gr
gr
lb

The formula

FOC % = ((balance_point − arrow_length ÷ 2) ÷ arrow_length) × 100

  • Arrow length is measured AMO-style: from the throat of the nock to the end of the shaft, not including the point.
  • Balance point is measured on the finished arrow — point, insert, fletching, and nock all installed.
  • Total weight is the sum of shaft, point, insert, fletching, and nock in grains.
  • Grains per pound is total arrow weight divided by peak draw weight. Most bowhunting organizations treat 5 gpp as the minimum safe arrow for a given bow.

How to use the number

  • Target and 3D: 7–12% FOC keeps trajectory flat and forgiving downrange.
  • Hunting: 12–19% FOC is the common window for penetration without wrecking drop.
  • Extreme FOC (20%+): penetrates exceptionally well on heavy bone but drops fast past 30 yards and demands a matched spine.

Changing point weight moves FOC and spine at the same time. After any point-weight change, re-check spine with the arrow spine calculator and confirm with a bare-shaft test.

Sources

  • AMO/ATA standard for arrow length and front-of-center measurement.
  • Easton Archery technical guides: arrow selection and FOC.
  • Ashby Bowhunting Foundation penetration studies on EFOC and total mass.

Last reviewed: 2026-08-27.

Frequently asked questions

What is arrow FOC?

Front of center is the percentage of the arrow's total length that the balance point sits ahead of the physical center. A 30-inch arrow balancing 1.5 inches ahead of center has 5% FOC. Higher FOC pushes more mass toward the point.

What FOC should I shoot?

Target and 3D archers typically run 7-12% FOC for a flat, forgiving trajectory. Hunters commonly run 12-19% for penetration and quieter flight. Extreme FOC above 20% is a specialty setup — it penetrates hard but drops fast past 30 yards.

How do I measure the balance point?

Build the arrow complete — point, insert, shaft, fletching, and nock — then balance it on a narrow edge until it sits level. Measure from the throat of the nock to that balance point. That distance is what this calculator needs.

Does total arrow weight matter as much as FOC?

Yes. Momentum drives penetration, and momentum comes from total grain weight and speed. Most bowhunting authorities want at least 5 grains of arrow per pound of draw weight; the calculator flags your grains-per-pound so you can check both numbers at once.

Can I cite this?

Yes. Link to https://wild10.com/tools/arrow-foc-calculator. The AMO formula is published on the page.