# What is my arrow’s FOC?

Works out an arrow’s front of center (FOC) percentage from its length and balance point, with Easton’s recommended ranges for target and hunting arrows.

- Page: https://www.acalculator.org/sports/foc-calculator
- JSON spec: https://www.acalculator.org/sports/foc-calculator.json
- Version: dfc7db90dbe3

## Default answer

Example with the default inputs (Arrow length (L) 29 in, Balance point (A) 16.5 in): An arrow 29 in long that balances 16.5 in from the nock has an FOC of 6.9%.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| l | Arrow length (L) | From the bottom of the nock groove to the end of the shaft, not including the point. |
| a | Balance point (A) | From the nock throat to the point where the finished arrow balances on an edge. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| foc | FOC | Front of center: how far the balance point is ahead of the middle, as a percent of the length. |
| center | Center of the arrow (L ÷ 2) | Half the arrow length, measured from the nock throat. |
| ahead | Balance point ahead of center | A − L ÷ 2: how far the balance point is in front of the middle. |

## Method

FOC % = 100 × (A − L ÷ 2) ÷ L, with L the arrow length (nock groove to end of shaft) and A the balance point from the nock throat.

## Assumptions

- Measure the finished arrow with its point, insert, nock and fletching in place.
- L does not include the point; A is measured from the same end (the nock throat).
- A balance point behind the middle gives a negative FOC.

## Worked examples

1. l = 0.7366, a = 0.4191 gives foc = 6.896552%, center = 0.3683. Source: Easton Archery, What is F.O.C. and how does it affect arrow flight? (halve the arrow length, measure the balance point from the nock throat, subtract, multiply by 100, divide by the length). https://eastonarchery.com/2014/06/foc/, retrieved 2026-10-02.
2. l = 0.7112, a = 0.4445 gives foc = 12.5%. Source: 3.5 × 100 ÷ 28 = 12.5%, in the hunting range of Easton Archery, FAQs about arrow F.O.C. (front of center): 7–15% indoors, 10–15% outdoors and for hunting. https://eastonarchery.com/2022/03/faqs-about-arrow-f-o-c-front-of-center/, retrieved 2026-10-02.
3. l = 0.762, a = 0.4953 gives foc = 15%, ahead = 0.1143. Source: Easton Archery, What is F.O.C. and how does it affect arrow flight? (halve the arrow length, measure the balance point from the nock throat, subtract, multiply by 100, divide by the length). https://eastonarchery.com/2014/06/foc/, retrieved 2026-10-02.

## FAQ

### What is arrow FOC?

FOC, front of center, is how far an arrow’s balance point sits ahead of its middle, as a percent of the arrow’s length. More weight up front (a heavier point or insert) raises the FOC.

### How do I calculate FOC?

Halve the arrow length L, subtract that from the balance point A (measured from the nock throat), multiply by 100 and divide by L: FOC = 100 × (A − L/2) ÷ L. A 28 in arrow balancing at 17.5 in has 100 × (17.5 − 14) ÷ 28 = 12.5% FOC.

### How do I measure the arrow length and balance point?

Use the finished arrow with the point, insert, nock and vanes on. L runs from the bottom of the nock groove to the end of the shaft, without the point. Balance the arrow on a thin edge and measure A from the nock throat to that spot.

### What FOC should my arrows have?

Easton recommends 10–15% for hunting arrows, 7–15% for indoor target arrows and 10–15% for outdoor target arrows. Higher FOC helps arrows fly steady and hold their line downrange.

### How do I raise my FOC?

Add weight at the front: a heavier point, a heavier insert or a weight collar. Lighter vanes and nocks at the back also move the balance point forward a little.

### Can FOC be negative?

Only if the balance point is behind the middle of the arrow, which is rare for a finished arrow. The calculator shows a negative percent in that case.

## Sources

- Easton Archery, What is F.O.C. and how does it affect arrow flight? (divide the length, from the bottom of the nock groove to the end of the shaft, by 2; find the balance point and measure it from the nock throat; subtract; multiply by 100; divide by the length; 10–15% for hunting). https://eastonarchery.com/2014/06/foc/ (retrieved 2026-10-02)
- Easton Archery, FAQs about arrow F.O.C. (front of center): 7–15% indoors and 10–15% outdoors for target arrows, 10–15% for hunting. https://eastonarchery.com/2022/03/faqs-about-arrow-f-o-c-front-of-center/ (retrieved 2026-10-02)