Arrow FOC Calculator (Archery)

FOC stands for Front of Center and refers to how far forward the center of gravity of an arrow is from the geometric center of the arrow. It is expressed as a percentage. A higher FOC means more weight toward the tip, which generally improves arrow stability and penetration.

The standard AMO formula is: FOC% = ((B − L/2) / L) × 100, where L is the total arrow length and B is the balance point distance, both measured from the nock throat. Enter those two measurements into this calculator and it will compute the result for you.

A properly balanced arrow typically has an FOC between 7% and 15%. Arrows in this range offer good stability and accuracy. Bowhunters often prefer the higher end (10%–15%) for better penetration on big game, while target archers may tune toward the lower end for flatter trajectory.

An FOC that is too low (under 7%) can cause the arrow to fishtail or plane erratically in flight. An FOC that is extremely high (above 15%) may cause the arrow to nose-dive and lose range. The 7%–15% sweet spot balances stability with trajectory performance.

Place the arrow on a flat edge (like a finger or a pencil) and slide it until the arrow balances horizontally without tipping. The point where it balances is the center of gravity. Measure from the nock throat to that point to get your balance point distance.

Arrow length is measured from the nock throat (the groove where the string sits) to the very end of the shaft — not including any point or tip that extends beyond. Likewise, the balance point distance is measured from the same nock throat reference.

You can increase FOC by using a heavier point or insert, adding a weight screw inside the front of the shaft, shortening the shaft, or using lighter nocks and vanes. Each change shifts the center of gravity forward and raises the FOC percentage.

FOC matters for both disciplines but is prioritized differently. Bowhunters focus heavily on FOC for penetration and reliable arrow flight at varying angles. Target archers also tune FOC for consistent grouping, though they may accept lower values to preserve a flatter trajectory at long distances.