Arrow FOC Calculator

Front of Center (FOC) is calculated by finding the balance point of a fully assembled arrow and comparing it to the total physical length of the arrow shaft. The standard industry formula is expressed as:

FOC (%) = [ (Balance Point - (Total Length / 2)) / Total Length ] × 100

First, measure the total length of the arrow from the bottom of the nock groove to the end of the shaft (excluding the point length for standard IMS metrics, or including it depending on your measurement convention, though total carbon length is most reliable). Next, find the exact balance point by resting the arrow on a pivot edge. Finally, apply the formula to determine how far forward the center of mass sits relative to the true geometric center of the arrow.

Imagine you are building a custom carbon arrow for target archery. You take the following measurements:

Total Arrow Length: 30 inches
Balance Point (Distance from nock groove to balance edge): 19 inches

Step 1: Divide the total arrow length by 2 to find the geometric center. 30 inches / 2 = 15 inches.

Step 2: Subtract the geometric center from the balance point measurement. 19 inches - 15 inches = 4 inches.

Step 3: Divide that difference by the total arrow length. 4 inches / 30 inches = 0.1333.

Step 4: Multiply by 100 to convert to a percentage. 0.1333 × 100 = 13.33%.

Your arrow features an FOC of 13.33%, which falls comfortably within the ideal range for reliable outdoor target flight.

Always weigh and measure your arrows with all components installed, including the nock, vanes, insert, and broadhead or field point, as missing components will skew the balance point. Target archers typically prefer an FOC between 10% and 15% for flat trajectories at longer distances, while bowhunters often seek 15% to 20% or higher to maximize penetration and bone-breaking momentum upon impact. Avoid extreme FOC changes without re-testing your bow sight marks, as heavier front ends will cause arrows to impact lower at longer distances.