Foc Calculator - Arrow Balance and Front-of-Center

An arrow foc calculator is a tool that converts an arrow's total length and the distance to its static balance point into a single percentage called front of center (FOC), which describes how much of the arrow's mass sits ahead of its geometric midpoint.

• • Tune a hunting setup: Pick a broadhead weight that pushes the FOC into the 10-15% hunting band so the arrow flies straight on impact and penetrates well.
• • Validate a target archery build: Confirm that indoor and 3D arrows sit in the higher target band so the spine and point match the round you shoot.
• • Compare two arrow builds: Run the same shaft length with different point weights to see how each change shifts the FOC before you buy components.
• • Diagnose a back-of-center arrow: Spot a negative or near-zero FOC when broadheads plan off or groups open up, then add point weight or shorten the shaft to fix it.

Archers who shoot the same setup for years often settle into an FOC range without ever measuring it, then run into broadhead flight problems when they swap components. An arrow foc calculator removes the guesswork by turning two measurements - the arrow length and the balance point - into a number you can compare to published bands.

Most published guides group FOC into a hunting band near 10-15%, a target band that often runs higher, and a low band below about 7% that produces wobbly flight. The calculator below reads both inputs in centimeters or inches, runs the standard front-of-center formula, and prints the band so you know what to do next.

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The calculator applies the standard front-of-center formula to the arrow length (A) and the balance point distance (B), then rounds the result to one decimal place and labels it with a recommended band.

• A: Total arrow length from the back of the nock to the tip of the point or broadhead. Enter the same unit as the balance point.
• B: Distance from the back of the nock (throat) to the static balance point of the finished arrow, measured with the broadhead or target point installed.
• Unit System: Centimeters or inches. Both inputs share this selector so the formula divides matching units.

The math only takes three steps: subtract half the arrow length from the balance point, divide by the arrow length, and multiply by 100 to get a percentage. The calculator does all three steps instantly and also prints the balance offset - the distance in your selected unit between the geometric center of the arrow and the balance point - because many archers find that number easier to reason about than the percentage.

Because the formula divides two values in the same unit, the calculator locks both inputs behind one unit selector. If you measure an arrow in inches, keep B in inches too. Mixing units throws the percentage off by a factor of 2.54 and produces a useless reading.

According to Easton Archery, front of center is calculated by subtracting half the arrow length from the distance to the balance point, dividing that remainder by the total arrow length, and multiplying by 100 to get a percentage.

According to Omni Calculator, a 30 cm hunting arrow with an 18 cm balance point has a 10% front of center, which sits in the recommended hunting band.

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Four ideas sit behind the FOC percentage. Understanding them helps you turn the calculator's output into a setup change.

Front of center is a percentage, not an absolute weight. The same 12% FOC can come from a 30-inch wood shaft with a 200-grain point or a 27-inch carbon shaft with a 100-grain point - the formula does not care about mass, only about where the balance point sits relative to the geometric center.

The static balance point is a single measurement, not a moving target. Once a point and broadhead are installed, the balance point stays put as long as you do not swap components. The calculator therefore gives the same answer every time for the same arrow build.

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Measure your arrow once, type the two numbers into the calculator, and read the percentage and the recommended band in the results panel.

1. 1 Choose a unit system: Pick centimeters if you measured with a metric ruler or inches if you used an imperial arrow scale. The selector applies to both inputs.
2. 2 Measure the total arrow length: Measure from the back of the nock to the tip of the point or broadhead, then enter it in field A.
3. 3 Measure the balance point: Balance the finished arrow on your finger or a balance scale and measure from the back of the nock to that point, then enter it in field B.
4. 4 Read the FOC percentage: The big number at the top of the results panel shows the front-of-center percentage to one decimal place.
5. 5 Compare to the recommended band: The recommended band label below the percentage tells you whether the FOC is too low, in the hunting zone, or in the target zone.
6. 6 Adjust the build and re-run: Swap point weights or trim the shaft, then re-measure and re-run the calculator until the FOC sits in the band that matches your shooting style.

An archer with a 32-inch carbon shaft and a 100-grain target point balances the arrow at 16.5 inches from the nock. Entering A = 32 and B = 16.5 returns a 3.1% FOC with the 'below the hunting band' label. After swapping in a 125-grain point the balance point moves to 17.0 inches and the calculator returns a 6.3% FOC, still below the hunting band but moving in the right direction. A 150-grain point pushes the balance point to 17.75 inches and lands the arrow at a 10.9% FOC, which the calculator flags as 'hunting band (10-15%)'.

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Running numbers before you shoot saves broadheads, target points, and range time.

• • Faster broadhead tuning: Skip the trial-and-error of swapping broadheads at the range by predicting the FOC before the first shot.
• • Clear target vs hunting setup: See the difference between a target setup and a hunting setup on the same arrow so you can decide which build to assemble.
• • Catch back-of-center arrows early: Spot a negative or near-zero FOC before it ruins a hunt or an indoor scorecard.
• • Compare component swaps in seconds: Try lighter or heavier points in your head and watch the FOC shift without rebuilding the arrow each time.
• • Shareable scouting numbers: Quote a percentage with a teammate or coach instead of describing where the arrow balances on a finger.

The calculator also documents the setup. A written FOC percentage tells another archer exactly how your rig is tuned, which is more useful than 'it balances a bit forward of center'.

Because the formula is dimensionless, the calculator works equally well for wooden target shafts, aluminum practice shafts, and modern carbon hunting arrows. The math does not care what the arrow is made of.

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Four variables change an arrow's FOC. Two more caveats limit how far you can push the percentage.

• • The formula assumes a static balance point measured with the broadhead installed. It does not account for arrow flex in flight, which also influences stability at full draw.
• • FOC is one of several tuning numbers. Spine, draw weight, point alignment, and broadhead design all matter alongside the percentage.

An arrow with the right FOC still needs the right spine for the bow. Treat the percentage as one input into a tuning workflow rather than the final answer.

The calculator rounds the percentage to one decimal place. Most archers treat changes smaller than about 0.5 percentage points as noise, so do not chase fractions that fall inside that tolerance.

According to Wikipedia, archery is the art, sport, practice, or skill of using a bow to shoot arrows, and the weight and balance of an arrow influence its stability and accuracy in flight.