What Is Arrow FOC?
Front of Center (FOC) describes how much of an arrow's total weight sits toward the front (point) half of the shaft. Expressed as a percentage, it tells you where the arrow's balance point falls relative to its physical center. A higher FOC moves the balance point forward, which generally improves forgiveness and downrange stability but can drop trajectory; a lower FOC flies flatter but may be less stable. This calculator works for any arrow setup—hunting or target—using universal inches.
How to Use It
Measure the arrow length from the throat (deepest part) of the nock groove to the end of the shaft (do not include the point that protrudes). Then balance the fully built arrow—point, insert, fletching, and nock installed—on a thin edge and measure the balance point from the same nock groove. Enter both values and the calculator returns your FOC percentage.
The Formula Explained
$$\text{FOC \%} = \frac{\text{Balance Point (in)} - \dfrac{\text{Arrow Length (in)}}{2}}{\text{Arrow Length (in)}} \times 100$$ The term \(\dfrac{\text{Arrow Length (in)}}{2}\) is the physical center of the shaft. Subtracting it from the balance point gives how far forward of center the arrow balances; dividing by the full length and multiplying by 100 normalizes that distance into a percentage.
Worked Example
An arrow is 29 inches long and balances 18 inches from the nock. Center is \(29 \div 2 = 14.5\) in. $$\text{FOC} = \frac{18 - 14.5}{29} \times 100 = \frac{3.5}{29} \times 100 \approx 12.07\%$$—a typical hunting FOC.
Typical FOC Ranges by Discipline
Front of Center (FOC) describes how much of an arrow's total weight sits forward of its physical center. It is expressed as a percentage of arrow length and is calculated with:
$$\text{FOC \%} = \frac{\text{Balance Point} - \dfrac{\text{Arrow Length}}{2}}{\text{Arrow Length}} \times 100$$There is no universal "best" number — the ideal range depends on what you are trying to optimize. The commonly cited ranges are summarized below.
| FOC Range | Discipline / Use | Purpose It Serves |
|---|---|---|
| 7–12% | Target & field archery (indoor, 3D, NFAA/World Archery) | Flatter trajectory and predictable grouping at known distances; lower FOC keeps arrows fast and forgiving of small form errors at paper targets. |
| 10–15% | Standard hunting / general broadhead setups | A balance of stable broadhead flight, reasonable trajectory, and good penetration on game — the most widely recommended window for bowhunters. |
| 15–19%+ | High FOC and Extreme FOC (EFOC/Ultra-EFOC) | Maximizes penetration and steers heavy broadheads in wind; favored for big-game and traditional setups where deep penetration outweighs flat trajectory. |
As a reference point, the Easton-style "normal" FOC for hunting arrows has long been quoted around 10–15%. Pushing much above 19% (often called Ultra-EFOC) can sharpen penetration further but steepens arrow drop and demands careful tuning.
Interpreting Your FOC Result
Your FOC percentage tells you how nose-heavy your arrow is, which influences four practical performance traits:
- Stability & steering: Higher FOC puts more mass up front, so the arrow's fletching has more leverage to steer it and correct in flight. This helps stabilize fixed-blade broadheads and resist wind drift.
- Forgiveness: Moderate-to-high FOC can make flight more consistent and tolerant of slight form errors, but extremely high FOC can over-correct and become twitchy if the rest of the setup (spine, fletching) is not matched.
- Penetration: A forward weight bias concentrates momentum behind the point, which generally improves penetration — a key reason hunters favor higher FOC.
- Trajectory drop: Higher FOC usually means a heavier, slower arrow that drops faster downrange, so you give up flatness and need more precise range estimation. Lower FOC keeps arrows faster and flatter for known-distance target work.
Low FOC (roughly below 7–8%): Fast and flat, but can be harder to stabilize with broadheads and may show fish-tailing. High FOC (15%+): Excellent steering and penetration, but steeper arrow drop. Mid-range (10–15%): The all-around compromise most hunters use.
There is no single "correct" FOC value. The right number depends on your goal — flat, fast scoring arrows versus deep-penetrating, wind-stable hunting arrows — and must be tuned together with arrow spine, point weight, and fletching. Treat your FOC result as one input in overall arrow tuning, and confirm real-world results with broadhead flight and grouping at distance.
FAQ
What is a good FOC? Target archers often run 7–12%, while many hunters prefer 12–19% for deeper penetration. There is no single "correct" value—match it to your goals.
How do I raise my FOC? Add weight to the front (heavier points, brass inserts) or lighten the rear (smaller fletching, lighter nock).
Where do I measure arrow length from? From the nock groove throat to the end of the shaft, not the tip of the point.
