MasterTool

Arrow FOC Calculator

Calculate an arrow's front-of-center (FOC) percentage from its length and balance point.

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What this tool does

Calculate an arrow's front-of-center (FOC) percentage from its length and balance point. Measure the balance point by balancing the finished arrow (point, insert, fletching and nock fitted) on a knife edge. FOC changes with point weight, insert and fletching choices.

How to use the Arrow FOC Calculator

  1. Enter or select total arrow length (inches).
  2. Enter or select balance point from the nock throat (inches).
  3. Read the calculated result; change any measurement to compare alternatives.

Formula

FOC % = (balance point − arrow length ÷ 2) ÷ arrow length × 100, with all measurements in inches from the nock throat (the standard AMO method)
length
Total arrow length (inches)
balance
Balance point from the nock throat (inches)

Measure the balance point by balancing the finished arrow (point, insert, fletching and nock fitted) on a knife edge. FOC changes with point weight, insert and fletching choices.

Worked example

For arrow foc calculator, the following measurements illustrate the exact method: Total arrow length (inches): 29; Balance point from the nock throat (inches): 18.

Inputs

  • Total arrow length (inches)29
  • Balance point from the nock throat (inches)18

Result

  • FOC (%)12.07
  • Balance point ahead of centre (inches)3.5
  • ClassificationStandard — typical hunting / 3D range

Results explained

FOC (%)
FOC (%) from the formula above. Measure the balance point by balancing the finished arrow (point, insert, fletching and nock fitted) on a knife edge. FOC changes with point weight, insert and fletching choices.
Balance point ahead of centre (inches)
Balance point ahead of centre (inches) from the formula above. Measure the balance point by balancing the finished arrow (point, insert, fletching and nock fitted) on a knife edge. FOC changes with point weight, insert and fletching choices.
Classification
Classification from the formula above. Measure the balance point by balancing the finished arrow (point, insert, fletching and nock fitted) on a knife edge. FOC changes with point weight, insert and fletching choices.

Frequently asked questions

Most bowhunters aim for 10–15%. Higher FOC improves stability and penetration momentum, but past ~19% trajectory drops faster and spine/tune problems appear.

Often 7–11% — enough for stability without the steep trajectory of a heavy hunting build, since target distances are known and wind drift matters more than penetration.

Add point or insert weight, use a lighter shaft or shorter arrow, or lighter fletching. Every change also affects dynamic spine, so re-check tune after adjusting.

The AMO standard measures from the nock throat (where the string sits) to the balance point, and total length the same way, so FOC figures are comparable between archers and brands.

Yes, if the balance point sits behind the arrow's midpoint — usually a sign of heavy fletching or a very light point on a short arrow. It generally flies poorly and is worth correcting.