Balance the finished arrow (point on) across a knife edge or your finger, and measure from the bottom of the nock slot to that spot.
11.4 % FOC
Where that sitsHunting range
FOC calculator
FOC (front of center) tells you how far forward your arrow balances. More weight up front flies steadier and hits harder, but drops more. Measure your balance point, or estimate it from your arrow’s parts, and see where your arrow sits: target range, hunting range or extreme.
How to use it: Balance your finished arrow on a knife edge, measure from the bottom of the nock slot to that spot, and set the two sliders. No arrow to hand? Switch to “estimate from parts”.
// The calculator
// The math
How it’s calculated
FOC % = (balance point − length ÷ 2) ÷ length × 100. Length runs from the nock throat to the end of the shaft (16–32″, so crossbow bolts fit too), and the balance point is measured from the nock throat (Easton’s method).
No arrow to balance yet? The parts mode estimates the balance point from each part’s weight and where it sits: the shaft at its middle, point and insert at the front, the nock at the throat, vanes about 3″ up. Easton recommends 10–15% for hunting; 19% and up is extreme FOC in Dr. Ed Ashby’s studies.
A worked example
A 28.5″ arrow that balances 17.5″ from the nock throat: (17.5 − 14.25) ÷ 28.5 × 100 = 11.4% FOC, in the hunting range.
The full explanation: Find the FOC of your crossbow bolts.
// FAQ
Questions about FOC
Quick answers about measuring FOC, good ranges and how to change it.
What is a good FOC?
Easton recommends 10–15% for hunting arrows. Target and practice arrows often sit around 7–10%. Dr. Ed Ashby’s penetration studies call 19% and up “extreme FOC”.
How do I raise my FOC?
Put weight up front: a heavier point, a brass or steel insert, or a weight collar. Lighter vanes help a little. Heavier points make the arrow act weaker, so recheck your spine.
Where exactly do I measure from?
Arrow length runs from the bottom of the nock slot (the throat) to the end of the shaft, without the point. Balance the finished arrow, point on, and measure from the nock throat to the balance spot.
// More tools
Arrow weight builderTotal grains and grains per pound for your arrow.Open tool →Arrow spine finderA starting spine for your setup.Open tool →Arrow energy calculatorEnergy and momentum from arrow weight and speed.Open tool →Crossbow bolt weight checkerYour bolt against your crossbow’s minimum weight.Open tool →
