Arrow FOC Calculator: Front of Center Percentage
Enter your arrow's total length and the distance from the nock throat to the balance point. The calculator gives you the front-of-center (FOC) percentage, classifies it against the standard archery bands, and shows the math step by step. Switch between inches and centimetres. Defaults produce a working result straight away.
Formula
Worked example
An arrow 28 in long with a balance point 17.5 in from the nock throat: midpoint = 28 / 2 = 14 in; offset = 17.5 - 14 = 3.5 in; FOC = (3.5 / 28) x 100 = 12.5%. This falls in the recommended hunting range of 11-18%.
What is arrow FOC and why does it matter?
Front of Center (FOC) is the percentage of an arrow's weight that is concentrated in the front half of the shaft. A higher FOC means the center of gravity sits further forward of the arrow's geometric midpoint. This forward weighting makes the arrow self-correct in flight: drag from the vanes at the rear straightens any wobble more aggressively when the front is heavier. The practical result is tighter groups at medium distances, better performance through wind, and more consistent broadhead flight. For bowhunters, a higher FOC also drives deeper penetration because the front-heavy mass transfers energy more directly into the target on impact.
How to measure your arrow for FOC
Attach every component that will be on the arrow when you shoot: nock, vanes, insert, and point or broadhead. Measure the total length (A) from the bottom of the nock groove to the far end of the shaft, not including the point. Then balance the arrow on a finger or a thin dowel and mark that balance point. Measure from the nock throat to the balance point; this is B. Enter both into the calculator above. If you change any component, including switching from field tips to broadheads or swapping vane size, remeasure because even a few grains shift the balance point noticeably.
How to adjust your arrow's FOC
The simplest way to raise FOC is to add weight at the front: a heavier insert (brass inserts run around 100 grains vs about 16 grains for aluminium), a heavier point or broadhead, or a weighted insert screw. Reducing weight at the rear also helps: lighter nocks, shorter vanes, or switching from plastic to feather fletching. To lower FOC, do the reverse: move to a lighter field point, add a heavier nock, or use longer vanes. Keep in mind that adding front weight stiffens the dynamic spine of the arrow, which may require switching to a stiffer shaft to maintain good tune. Every FOC adjustment should be followed by paper tuning or a bare-shaft test.
FOC and kinetic energy: the full picture
FOC tells you where the weight is, not how much total energy the arrow carries. A high-FOC arrow with very little total mass may still lack the kinetic energy needed for clean, ethical kills on large game. Easton Archery recommends at least 25-41 foot-pounds of kinetic energy for deer-sized game and 42-65 for elk and black bear. Use a kinetic energy calculator alongside this tool. The ideal hunting setup balances adequate total arrow weight, sufficient bow speed to deliver that energy at distance, and an FOC percentage that keeps flight stable and penetration deep.
FOC ranges by archery use case
| FOC range | Category | Typical use case | Flight effect |
|---|---|---|---|
| Below 7% | Too low | None recommended | Erratic, tail-heavy flight |
| 7-11% | Standard / target | Target, 3-D, indoor | Flat trajectory, less penetration |
| 11-15% | Recommended hunting | Field and broadhead hunting | Balanced flight and penetration |
| 15-18% | High hunting | Big game bowhunting | Improved penetration, slight arc |
| 18-30% | High FOC | Long-range or pass-through priority | Steeper drop, maximum penetration |
| Above 30% | Extreme FOC | Specialty setups only | Pronounced arc, difficult to tune |
Standard front-of-center guidelines. Easton Archery recommends a minimum of 10-15% for hunting arrows.
Frequently asked questions
What is a good FOC percentage for a hunting arrow?
Most bow-hunting authorities recommend 11-18% FOC for hunting arrows with broadheads. Easton Archery specifically calls 10-15% the minimum standard. Many modern bowhunters chase 15-20% or higher for maximum penetration on big game, accepting a slightly steeper trajectory in exchange for more reliable pass-throughs.
Does FOC affect broadhead accuracy?
Yes, noticeably. Broadheads act like small wings and can steer an under-stabilised arrow off course. A higher FOC damps broadhead-plane effects by making the arrow more self-correcting. Archers who switch from field tips to fixed-blade broadheads and see group dispersion often find that raising FOC brings groups back together without changing draw weight or arrow spine.
Can FOC be too high?
Yes. Beyond about 25-30%, the extra nose weight causes the arrow to nosedive steeply, producing a pronounced arc that makes ranging and aiming at distance more difficult. It can also over-stiffen the dynamic spine, causing tuning problems. The sweet spot for most hunting setups is 12-20%: enough forward bias for stable, penetrating flight without sacrificing a flat enough trajectory to be useful at realistic bowhunting distances.
Does FOC change when I switch from field tips to broadheads?
Almost always. If your broadhead weighs more than your field tip, FOC goes up; if it weighs the same, FOC stays constant. Many bowhunters use 100-grain field tips to match 100-grain broadheads, keeping FOC identical between practice and hunting. If you use a heavier broadhead, measure FOC again with the broadhead attached to know your true hunting setup.
What is the FOC formula?
FOC% = ((B - A/2) / A) x 100, where A is the total arrow length measured from the nock throat to the shaft end, and B is the distance from the nock throat to the balance point. The numerator is how far the balance point sits ahead of the shaft's geometric midpoint; dividing by total length and multiplying by 100 expresses that offset as a percentage.
Should I measure FOC with or without the broadhead?
With. FOC is only meaningful when every component is in place: nock, vanes, insert, point or broadhead, and any wraps. The broadhead or field point often contributes the largest single mass item on the front of the arrow and has the greatest effect on where the balance point lands. Measuring with just the shaft gives a number that does not reflect how the arrow will actually fly.