What FOC means
Front of center (FOC) describes how far an arrow’s balance point sits ahead of its physical middle, as a percentage of its length. A higher FOC puts more weight at the front, which helps the arrow fly straight and recover from launch disturbances.
FOC (%) = (balance point − length ÷ 2) ÷ length × 100
How to measure
- Measure the arrow length from the throat of the nock (where the string sits) to the end of the shaft, not including the point.
- With the point installed, balance the complete arrow on a thin edge and mark the balance point.
- Measure from the nock throat to the balance point.
Example
A 29 in arrow balancing 16.5 in from the nock throat:
- center: 14.5 in;
- FOC: (16.5 − 14.5) ÷ 29 ≈ 6.9%.
Recommended ranges
- Target archery: often 7 to 12%. Outdoor target archers often aim for 10 to 15%.
- Hunting: 10 to 15% is common. Some hunters build 15 to 20% “high-FOC” or “extreme-FOC” setups to improve penetration with heavy points.
- Below 7%: arrows can be less stable, especially with broadheads.
To raise FOC, use a heavier point, a heavier insert or brass insert weights, or lighter vanes and nock.
Arrow weight and GPP
The total arrow weight is the shaft weight (grains per inch × length) plus the point, insert, nock and fletching. Dividing by the bow’s draw weight gives grains per pound (GPP):
- under 5 GPP: too light for most bows; it can damage the bow like a dry fire. Many manufacturers set a minimum of 5 to 6 GPP.
- 6 to 8 GPP: a common hunting and 3D range, balancing speed and energy.
- 8 GPP and more: heavier arrows are quieter and carry more momentum, but are slower.
In the example, 9 GPI × 29 in + 140 gr of components = 401 grains; with a 50 lb bow, that is about 8.0 GPP.
Spine matters too
Adding point weight makes the arrow act weaker in spine. A big change in point weight may require a stiffer shaft; check the manufacturer’s spine chart and paper-tune or bare-shaft-tune after changes.