What is my arrow’s FOC?
Measure your finished arrow’s length and where it balances. The calculator gives its FOC (front of center) percent and where that falls in Easton’s recommended ranges.
- FOC
- 6.9%
An arrow 29 in long that balances 16.5 in from the nock has an FOC of 6.9%.
Under 7%: low front weight
- Under 7%: low front weight
- 7–10%: Easton’s indoor target range
- 10–15%: Easton’s hunting and outdoor range
- Over 15%: high FOC
- Center of the arrow (L ÷ 2)
- 14.5 in
- Balance point ahead of center
- 2 in
FOC: 6.9%. An arrow 29 in long that balances 16.5 in from the nock has an FOC of 6.9%.
How to calculate
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.
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%.
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.
- 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
Each example is checked against the calculator on every build.
- Arrow length (L) 29 in, Balance point (A) 16.5 in gives FOC 6.896552%, Center of the arrow (L ÷ 2) 14.5 in.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
- Arrow length (L) 28 in, Balance point (A) 17.5 in 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
- Arrow length (L) 30 in, Balance point (A) 19.5 in gives FOC 15%, Balance point ahead of center 4.5 in.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
How it works
Easton’s FOC steps, written as one formula:
FOC % = 100 × (A − L ÷ 2) ÷ L
- L is the arrow length from the bottom of the nock groove to the end of the shaft. The point is not included.
- A is the distance from the nock throat to the balance point of the finished arrow.
- L ÷ 2 is the center of the arrow, and A − L ÷ 2 is how far the balance point is ahead of it.
The verdict uses Easton’s ranges: 7–10% (indoor target), 10–15% (hunting and outdoor target), under 7% and over 15%. The band edges follow the shown value (one decimal): 6.95% shows as 7.0% and counts as 7–10%, 15.04% shows as 15.0% and counts as 10–15%.
Rules
- L and A are each more than 0 and at most 5 m; type them in in, cm or mm.
- A balance point past the end of the length (A > L) gives no answer. Two lengths that differ by less than one part in 10¹² count as equal, so 29 in and 73.66 cm are the same length.
- A balance point behind the middle gives a negative FOC.
Output format. FOC to one decimal place; the center and the distance ahead of it to 6 significant figures, in inches (or cm in Metric).
Worked examples by hand
29 in arrow, balance point 16.5 in. Center = 29 ÷ 2 = 14.5 in. Ahead = 16.5 − 14.5 = 2 in. FOC = 2 × 100 ÷ 29 = 6.9%: just under the 7% low end.
28 in arrow, balance point 17.5 in. 17.5 − 14 = 3.5 in. FOC = 3.5 × 100 ÷ 28 = 12.5%: in the hunting range.
30 in arrow, balance point 19.5 in. 19.5 − 15 = 4.5 in. FOC = 4.5 × 100 ÷ 30 = 15.0%: the top of the hunting range.
Other questions people ask
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.