Arrow FOC Calculator for Crossbow Bolts
Enter your bolt length and balance point to get its front of center (FOC) percentage. How to measure both is explained below.
Calculator
Front of center
10.0 %
Reading
Typical range for crossbow bolts
Typical range for crossbow bolts. FOC is a description of balance, not a score; follow your bolt and crossbow maker's guidance.
The formula
FOC % = (balance point − length ÷ 2) ÷ length × 100. A 20-inch bolt balancing 12 inches from the nock end gives (12 − 10) ÷ 20 × 100 = 10 percent. See FOC and balance point in the glossary.
How to measure
- Fit the tip you will hunt or practise with.
- Balance the bolt on a thin edge, such as a ruler’s edge or a knife spine, until it sits level.
- Mark the balance point and measure from the nock end to the mark.
- Measure the bolt length from the nock end to the end of the shaft.
Using the result
Compare FOC alongside total weight and straightness. Our guide to FOC and crossbow accuracy explains what the number does and does not change, and how to choose crossbow bolts covers weight and length limits.
What to do with your result
Read nextBest crossbow boltsSee the bolts I tested, with weights, tolerances and prices.Read nextHow to choose crossbow boltsMatch length, weight and nock before you change point weight for FOC.Frequently asked questions
What is a good FOC for a crossbow bolt?
Many crossbow bolts land somewhere around 7 to 15 percent with a field point fitted. There is no single correct number; the bolt and crossbow maker’s guidance and how the bolt actually groups matter more than hitting a target figure.
Do I measure with the broadhead or field point on?
Measure with the tip you will shoot fitted, because the tip is the heaviest single component and it moves the balance point more than anything else. Re-measure if you switch tip weight or style.
Where do I measure the length from?
Measure from the nock end to the end of the shaft, not including the tip. Some makers measure from the nock groove, so check which method a published FOC figure uses before comparing.
How do I raise FOC?
A heavier tip or insert raises FOC most. Check that the total bolt weight still meets your crossbow’s minimum and stays within any maximum before changing anything.
More tools
See every calculator on the crossbow tools page.