How to determine the FOC manually. Take one of your arrows, fully equipped including tip, that you will be using. First you must find the balance point on the arrow's shaft. To do this try to balance the arrow on a sharp edge. Once you have successfully balanced the arrow, place some sort of mark at that spot on the arrow's shaft. Next, measure (inches) from the bottom of the nock grove to the balance point. Then measure (inches) the length of the arrow from the nock grove to the edge of the arrow shaft, not the insert (This is called the arrows cut length.) Divide the arrow length by two, this will give you the physical center of the shaft. Now subtract the physical center number from the balance point value and divide by the arrow length value. Multiple this number by 100 to get a percentage (%).

A FOC value range of 7-10 percent is widely used as the best for a good balance between arrow range and arrow flight stability. If your calculated FOC doesn't fall with this range, don't fret. You can still have good arrow flight with an FOC as high as 18 percent, but your range will not be as good. Try not to go below 7 percent.

Example FOC Calculation

Balance Point Length 17.25"
Arrow Length 28"
Arrow Length / 2 14"
Balance Point Length - (Arrow Length / 2) 17.25 - 14 = 3.25
3.25 divided by Arrow Length 3.25 / 28 = 11.6%