Well, there' s some controversy about how to calculate FOC. (Imagine that. Controversy among archers. LOL) One way is to measure the arrow from the bottom of the nock to the end of the insert. The other way is to measure from the bottom of the nock to the tip of the arrowhead. Then you divide the measurement by 2. Then balance the arrow, with head installed, over something (I just balance it over my finger but some people want to be more precise than that), mark the balance point and measure from the front end to the balance point. Then divide that measurement by half the arrow length and subtract from 1.

{{{Say you' ve got a 30" arrow and the arrow balances at 13" . 13/15 = .867 Then .867 - 1 = -13.3. FOC for that arrow is 13.3%.}}} - Don' t pay any attention to that mess. Like Howler so aptly pointed out below, it' s totally bogus. Don' t know what (or IF) I was thinking. I would delete it, but everybody should have the opportunity to see what he' s talking about. So, okay Howler. You caught me. Made my one mistake for the year.

Try this instead. Find the center of the arrow. Mark it. Find the balance point of the arrow. Mark it. Measure between the balance point and center point. Divide that measurement by the full length of the arrow.