FOC (Front of Center) Calculator
Front of Center (FOC) measures how far forward an arrow's balance point sits relative to its physical center. It directly affects arrow stability, trajectory, and penetration. Measure your arrow length and balance point, then select your intended use to see if your FOC is in the right range.
FOC is one of the most important factors in arrow tuning, yet many archers overlook it. The concept is simple: an arrow that is heavier toward the front flies more stably, like a dart. Too little FOC and the arrow wobbles or porpoises in flight. Too much and the arrow arcs excessively and loses speed faster.
The formula is: FOC% = ((balance point from nock - arrow length / 2) / arrow length) x 100. To find your balance point, rest the complete arrow (with point and fletching installed) on your finger or a narrow edge and find the spot where it balances perfectly.
For target archers, an FOC of 7-15% works well. The lower end gives a flatter trajectory, which helps at long outdoor distances, while the higher end provides more stability, which is useful in windy conditions and for indoor shooting. Most competitive target archers land around 10-12%.
Hunters generally want higher FOC, in the 15-20% range or even beyond. Dr. Ed Ashby's broadhead penetration studies showed that arrows with FOC above 15% consistently outperform lower-FOC arrows in bone-on-impact scenarios. Some extreme FOC (EFOC) setups for dangerous game go above 25%, using very heavy inserts and broadheads with light carbon shafts.
Adjusting FOC is done by changing the weight at either end of the arrow. Adding point weight (heavier inserts, brass weights behind the point) increases FOC. Adding weight at the back (heavier nocks, wrap-on weight) decreases FOC. Changing shaft length also affects the calculation.