Check a finished hunting arrow
Compare the measured FOC with Easton’s published 10–15% hunting recommendation.
FOC Calculator
Enter correct arrow length and finished balance point to get arrow front-of-center percentage and balance offset.
Calculate Arrow Front of Center
Measure from the bottom of the nock groove to the shaft end and to the finished arrow's balance point.
Your FOC percentage and balance offset will appear here.
How to Use FOC Calculator
1
Measure Correct Arrow Length
Measure from the bottom of the nock groove to the shaft end, excluding the point.
2
Find the Balance Point
Balance the finished arrow and measure from the same nock-groove reference.
3
Review FOC Context
Use the percentage as one tuning input alongside spine, total weight, clearance, and manufacturer guidance.
FOC Calculator Features
- AMO-standard FOC formula
- Unit-independent measurements
- Live midpoint and offset details
- Easton hunting-range comparison
Common Use Cases
Compare component changes
Rebalance after changing points, inserts, nocks, wraps, or fletching, then enter the new measured point.
Limits and Important Notes
Result type: Exact calculation
Calculation Details
- Measure correct arrow length from the bottom of the nock groove to the shaft end.
- Balance the finished arrow and measure to that point from the same nock reference.
- Compare the balance point with the shaft midpoint and divide the forward offset by arrow length.
Formula
FOC% = 100 × (A − L/2) ÷ L, where L is correct arrow length and A is balance point from the nock groove
Rounding
FOC displays to two decimal places.
Default Assumptions
- Both measurements use the same unit and the same nock-groove reference.
- The arrow is measured fully assembled with point, insert, nock system, and fletching.
- Balance point falls along the correct arrow length.
Verified Example
Inputs: 28-unit correct arrow length and 17-unit balance point.
Calculation: 100 × (17 − 14) ÷ 28 = 10.7143%.
Result: FOC = 10.71%.
Sources and Version
Version: AMO-standard F.O.C. balance formula
Last verified: 2026-08-13
Update responsibility: OnlineTool.me
- Easton Archery FAQs — What Is F.O.C.? — Easton Archery (accessed 2026-08-13)
- FOC alone does not determine arrow spine, dynamic tune, penetration, or safety.
- Easton’s 10–15% figure is a hunting-setup recommendation, not a universal pass/fail standard.
- Follow arrow and bow manufacturer specifications before changing component weight.
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