How to use the archery foc calculator
- Choose whether you know the balance point of the finished arrow or the weights of its parts, and the length unit.
- Enter the arrow length, measured from the throat of the nock to the end of the shaft without the point.
- For a measured balance point, enter the distance from the nock throat to where the arrow balances. For part weights, enter the weight of the shaft, insert, point, nock and fletching with the lengths of the insert and point.
- Read the front of center (FOC) percentage. In the advanced option, enter a target FOC to see the point weight that would reach it.
Formula
FOC % = 100 x (balance point - length / 2) / length
balance point = sum(weight x distance from nock throat) / total weight
point weight for a target: (B x W - M) / (x_point - B), where B = length x (0.5 + target / 100)
W and M are the total weight and the total moment of all parts except the point, and x_point is the distance of the point from the nock throat.
A 28 inch arrow
An arrow 28 inches long that balances 17.5 inches from the nock throat has an FOC of 100 x (17.5 - 14) / 28 = 12.50 percent. An arrow of 30 inches that balances at 15 inches has an FOC of exactly 0 percent.
From parts: a 300 grain shaft, a 20 grain insert 0.75 inch long, a 100 grain point 1 inch long, an 8 grain nock and 10 grains of fletching centered 3 inches from the nock throat. The balance point is 17.426 inches from the nock throat, the FOC is 12.23 percent and the arrow weighs 438 grains (28.38 g). To reach 12 percent, the point would weigh 97.4 grains.
What FOC tells you
Front of center describes how far the balance point sits ahead of the middle of the arrow. More FOC means more weight forward, which many archers use to steady flight and help an arrow recover from a rough release. The right amount depends on the bow, the arrow length, the shaft and the shooting style, so the number is a way to describe and repeat a setup, not a target for everyone.
Length conventions differ between sources. This page measures length from the throat of the nock to the end of the shaft, without the point, and treats the point as extra length. Use the same convention each time you compare.
Changing the setup safely
Adding weight to the point raises FOC and also lowers arrow speed and changes the spine behavior, so check your bow maker's limits for arrow weight and shaft stiffness before changing a point. A real balance test is the final word, since the model treats the shaft as evenly weighted and every other part as a point mass. For other target and sport scoring tools, see the bowling score calculator, the critical power model calculator and the powerlifting points calculator.
Assumptions and limits
- The shaft weight is spread evenly over its length. The insert, point, nock and fletching are single points at their centers.
- Distances are from the throat of the nock, and the point sits beyond the end of the shaft by half its length.
- Weights are in grains. One grain is 0.0647989 grams.
- A balance point more than one and a half arrow lengths from the nock is refused as a likely typing error.
Frequently asked questions
Is a higher FOC always better?
No. Very high FOC can make an arrow drop faster and need a stiffer shaft. Many archers settle on a value that groups well for their bow and keep it.
How do I find the balance point?
Rest the arrow on the edge of a ruler or a thin dowel and slide it until it balances, then measure from the throat of the nock to that spot.
Why does my number differ from another calculator?
Some sources include the point in the length or measure from the end of the nock. The result then shifts by a few percent. Use one convention consistently.
What if the target is not reachable?
The page says so when no point weight can reach the target FOC, for example when the point sits behind the target balance position.