Arrow FOC Calculator

Calculate an arrow’s front-of-center percentage from its finished balance point and arrow length.

Direct answer

Arrow front of center (FOC) describes how far the finished arrow’s balance point lies ahead of the midpoint of the defined arrow length, expressed as a percentage of that length.

To calculate FOC, measure:

Arrow length (A): from the throat of the nock to the end of the shaft, excluding the point.
Balance point (B): from the throat of the nock to the point where the fully assembled arrow balances.

Use the same linear unit for both measurements.

Calculator

How to interpret the result

FOC is a balance-location measurement, not a total-weight measurement.

For example, an FOC of 10% means the arrow’s balance point is forward of the midpoint by a distance equal to 10% of the defined arrow length. A larger positive FOC value means the balance point is farther forward relative to the midpoint; a smaller value means it is closer.

The number does not, by itself, tell you whether an arrow is correctly spined, tuned, or appropriate for a specific bow or use. This page does not prescribe a universal best FOC.

Formula

FOC (%) = 100 × (B − A/2) ÷ A

Where A is arrow length from the throat of the nock to the end of the shaft, excluding the point, and B is the balance-point distance from the same datum on the finished arrow.

Variables and units

Variable	Meaning	Units
A	Arrow length from nock throat to end of shaft	inches or centimeters
A / 2	Midpoint of the defined arrow length	same as A
B	Distance from nock throat to finished-arrow balance point	same as A
B − A / 2	Distance the balance point lies ahead of the midpoint	same as A
FOC	Front-of-center percentage	%

Because both distances use the same unit, the unit cancels in the ratio.

How to measure arrow FOC

Assemble the arrow being evaluated

Install the components that affect the finished balance point, including the point, insert or adapter, nock system, and fletching. If you change the configuration, measure the balance point again.

Measure arrow length (A)

Measure from the throat of the nock—the deepest part of the nock groove—to the end of the shaft. Do not include the point.

Find and measure the balance point (B)

Place the assembled arrow across a narrow edge and move it until it balances without tipping toward either end. Mark that location, then measure from the same nock-throat datum to the mark.

Keep the measurements consistent

The formula assumes both measurements use the same starting datum and length convention. Changing the datum changes the calculated result. FOC arrow length is separate from cut shaft length used for GPI-based weight calculation.

Worked example

Assume arrow length A = 28.5 in and balance point B = 17.0 in.

A/2 = 14.25 in
B − A/2 = 2.75 in
100 × 2.75 / 28.5 ≈ 9.65%

Calculated FOC: 9.65%

This is an example calculation, not a recommended target value.

Common mistakes

Measuring from the wrong nock location

Use the throat of the nock, or bottom of the nock groove, as the rear datum. Do not measure from the back edge of the nock.

Including the point in arrow length

For this convention, A ends at the end of the shaft. The point is not included.

Measuring an incomplete arrow

FOC describes the balance of the assembled configuration being evaluated. Adding or removing components can move the balance point.

Mixing measurement conventions or units

Measure A and B from the same datum. Inches and centimeters both work, but use the same unit for both measurements.

Treating FOC as total weight

FOC depends on where mass is located. Two arrows with the same total mass can have different balance points and different FOC values.

Limitations

FOC is a balance-location measurement, not a complete evaluation of an arrow setup. This calculator does not prescribe an ideal FOC or infer shooting performance from the percentage.

The result depends on measurement accuracy and the stated length convention. Errors in arrow length or balance-point location affect the calculated percentage.

How component changes affect FOC

FOC changes when the arrow’s mass distribution changes.

Change	Typical balance-point effect	Typical FOC effect
Add mass near the point end	Moves forward	Increases
Heavier point	Moves forward	Increases
Heavier front insert / adapter	Moves forward	Increases
Add mass near the nock end	Moves rearward	Decreases
Heavier nock system	Moves rearward	Decreases
Heavier rearward fletching / wrap	Moves rearward	Decreases

The exact numerical change depends on the mass, location, and rest of the arrow configuration. Total arrow weight and FOC are separate quantities: adding the same mass at different locations can produce the same total weight but a different balance point.

Arrow Weight Calculator
Estimate finished arrow mass from shaft GPI and installed component weights.
Reference
Component Measurements
Look up PAB component measurement conventions for points, adapters, collars, nocks, and fletching.
Arrow Components
Where an arrow's weight and balance come from, component by component.
Arrow Building & Consistency
Understand why physical arrows from the same nominal build may not finish identically.

How this relates to Precision Arrow Builder

This calculator answers the single-arrow balance question. Across a physical set, measured component differences can produce different weight and FOC outcomes depending on how those components are combined. Precision Arrow Builder is designed for that set-level problem, evaluating measured component inventory across complete arrow sets rather than only one finished-arrow measurement.

See how Precision Arrow Builder works

Arrow FOC questions

What is arrow FOC?

Arrow front of center, or FOC, describes how far the finished arrow’s balance point lies ahead of the midpoint of its defined arrow length, expressed as a percentage of that length.

How do you calculate arrow FOC?

Measure arrow length from the throat of the nock to the end of the shaft and measure from the same nock datum to the assembled arrow’s balance point. Then use FOC (%) = 100 × (balance point − arrow length / 2) ÷ arrow length.

How do you measure an arrow’s balance point?

Assemble the arrow, rest it across a narrow edge, and move it until it balances without tipping toward either end. Mark that location, then measure from the throat of the nock to the mark.

What increases arrow FOC?

Adding mass toward the point end generally moves the balance point forward and increases FOC. Adding mass toward the nock end generally moves the balance point rearward and decreases FOC.

Can two arrows with the same weight have different FOC?

Yes. Total weight measures how much mass the arrow has. FOC depends on where that mass is distributed, so equal-weight arrows can have different balance points and FOC values.

Is higher FOC always better?

This calculator does not assume that higher FOC is always better. FOC is one property of an arrow system; this page does not infer performance quality from the number.