Front of Centre (FOC)
How far forward the balance point sits, as a percentage of arrow length. More front weight generally steadies flight, at some cost to trajectory.
Calculator
Exclude the point. Inches and centimetres both work if B uses the same unit.
16.7% FOC
Balance point 19.0 in on a 28.5 in shaft.
Outside the commonly cited 7–15% range. Treat that range as a guide, not a rule.
How it works
Front of Centre says how far ahead of the midpoint the arrow balances. You find the balance point on a finished arrow, then compare it with half the shaft length.
The biggest source of wrong results is measuring L inconsistently. Always start at the nock groove and stop at the back of the point.
Formula
%FOC = 100 × (B − L/2) / L Estimate: B = Σ(mass × position) / Σ mass
Worked example
A 28.5 in shaft that balances 19.0 in from the nock groove is about 16.7% FOC. Mid-shaft balance is 0%.
FAQ
Is 7–15% required? No. It is a commonly cited working range. Hunting and target arrows often sit in different places inside or near it.
What does the parts estimate miss? Real balance depends on where each piece actually sits. Label it an estimate and check the built arrow.