🏹 Arrow FOC Percentage Calculator
Measure arrow length and balance point to determine front-of-center (FOC) percentage, evaluate tuning, and plan point weight adjustments.
Measure from nock groove to the end of the shaft (excluding point).
Support arrow on a dowel and measure distance from nock to balance point.
Weigh entire arrow with point, insert, fletching, wrap, and nock.
Include outserts, collars, or added weight screws.
FOC percentage
13.3%
Balanced FOC
Balance vs midpoint
Balance point 19.00″ • Midpoint 15.00″
Front offset: 4.00″ ahead of center
Front mass share
27.8%
Point mass 125 gr of 450 gr arrow
| Parameter | Value |
|---|---|
| Arrow length (L) | 30.00 in |
| Arrow midpoint (L/2) | 15.00 in |
| Balance point (B) | 19.00 in |
| FOC calculation | ((19.00 − 15.00) ÷ 30.00) × 100 = 13.3% |
How to Use This Calculator
Measure arrow length
Use a tape to measure from the throat of the nock to the end of the carbon shaft (excluding field point).
Find balance point
Place the arrow on a dowel or sharp edge and slide until it balances level, then measure from the nock to that point.
Fill in arrow mass details
Weigh the finished arrow and the point/insert assembly to understand front mass contribution.
Review FOC and recommendations
Use the qualitative guidance to decide if you should add or subtract point weight, inserts, or tail mass.
Formula
FOC (%) = ((Balance Point − (Arrow Length ÷ 2)) ÷ Arrow Length) × 100
Balance point (B) and arrow length (L) must be in the same units (inches).
Higher FOC shifts mass toward the point, improving stability and penetration, but excessive front weight can over-stress arrow spine and slow speed. Most hunting setups perform best between 10–15% FOC, while target archers often prefer 7–10%.
Arrow Tuning Tips
Adjusting FOC is part of tuning an arrow for consistent flight. Combine this calculation with spine selection, broadhead testing, and paper tuning to finalize your setup.
Ways to increase FOC
- Install heavier points, collars, ethical archery weight screws, or brass inserts.
- Shorten the shaft (within safe draw length limits) to reduce rearward mass.
- Use lighter vanes, wraps, or lighted nocks if FOC is too low.
When to decrease FOC
- If the arrow requires an excessively stiff spine or bareshaft tuning shows a weak node.
- When trajectory is too arced for 3D or field competition and speed matters more.
- If wind drift becomes a concern due to slow arrow speed.
Frequently Asked Questions
What FOC is best for bowhunting?
Common recommendations sit between 10–15%. Higher FOC (18–25%) can enhance penetration for heavy arrows and large game but may require stiffer shafts.
Does FOC affect broadhead flight?
Yes. Adequate FOC helps broadheads recover quickly off the string and resist planing in crosswinds. Too little FOC often causes erratic grouping.
Can I measure in centimeters?
Absolutely. Use the same units for length and balance point. The ratio remains the same; only the values change.
Do lighted nocks change FOC?
Yes. Heavier tail components shift balance rearward, reducing FOC. Re-check FOC whenever you change nocks or fletching.
How often should I recheck FOC?
Recalculate after altering point weight, inserts, nocks, fletching, or arrow length to ensure the setup still meets your goals.