Front of centre, almost always shortened to FOC, is the single number that describes where an arrow carries its weight. It is expressed as a percentage of the arrow's length, and it says how far ahead of the physical midpoint the arrow actually balances. An arrow with a heavy point and a light rear end balances well forward and has a high FOC. An arrow with a light point on a heavy shaft balances near the middle and has a low one. That balance governs how the arrow behaves after it leaves the string, and it is one of the few tuning variables an archer can change in five minutes with a different point.
This calculator takes the two measurements that define FOC — the arrow's length and its balance point — and returns the percentage, then adds up the component weights so you can see the finished arrow mass and the grains per pound of draw at the same time. Arb Digital builds these tools because the arithmetic is trivial and the mistakes are not: the most common error in archery forums is measuring arrow length to the tip of the point instead of the end of the shaft, which quietly inflates every FOC figure that follows.
What This Arrow FOC Calculator Does
It computes front of centre from the standard published definition used across the archery industry: the distance from the nock throat to the balance point, minus half the arrow length, divided by the arrow length, expressed as a percentage. That is the figure that shaft makers print in their tuning literature and the one that appears in setup guides from manufacturers such as Easton Archery, which has published arrow selection material since the 1950s.
Alongside the percentage it builds the arrow's weight from its parts. Shaft grains per inch multiplied by cut length gives the bare shaft. Add the point, the insert or collar system, and everything at the back — nock, wrap, fletching, glue — and you have the finished mass. Dividing that by the bow's peak draw weight gives grains per pound, the ratio that governing bodies and manufacturers use to set minimum arrow weights, and the breakdown bars show which third of the arrow is carrying the mass.
How to Use It
- Measure the arrow length correctly. From the throat of the nock — the deepest part of the groove the string sits in — to the cut end of the shaft. The point is not included. This is the definition the FOC formula assumes, and using overall length instead is the most common source of a wrong answer.
- Find the balance point. Rest the finished, fletched arrow across a thin straight edge and slide it until it sits level with no hand on it. Mark that spot and measure back to the nock throat.
- Enter the component weights. Grains per inch comes from the shaft box. Point weight is stamped or listed. Insert, collar, nock, wrap and fletching weights are all published by their makers, or you can weigh them on a grain scale.
- Enter the bow's peak draw weight. This changes nothing in the FOC calculation; it only produces the grains-per-pound figure in the results grid.
- Read the percentage and the finished weight together. Neither one is meaningful alone. A 19 per cent FOC on a 380-grain arrow and a 12 per cent FOC on a 600-grain arrow are two very different arrows.
The Formula and How It Is Calculated
The published relation is short. Let L be the arrow length from nock throat to the end of the shaft, and A be the distance from the nock throat to the balance point. Then:
FOC (%) = 100 × (A − L/2) ÷ L
Worked through with the values loaded on this page: a 29-inch arrow balancing 17.4 inches from the nock throat sits 17.4 − 14.5 = 2.9 inches ahead of centre. Divide 2.9 by 29 and multiply by 100 and you get exactly 10.00 per cent. The units cancel, which is why the answer is identical whether you measured in inches or centimetres, and why the unit selector on this page changes only the labels and the default numbers.
The weight side is simple addition: shaft grains per inch multiplied by cut length, plus point, plus insert hardware, plus the nock and fletching assembly. With the loaded values that is 9.5 × 29 = 275.5 grains of shaft, plus 100, plus 20, plus 30, for a finished arrow of 425.5 grains. Against a 60-pound bow that is 7.09 grains per pound.
What the Percentage Bands Actually Mean
Manufacturer literature and archery organisations describe FOC in loose descriptive bands rather than as a target to hit. Broadly, arrows balancing under about 7 per cent are described as low or neutral FOC, roughly 7 to 12 per cent as normal, 12 to 19 per cent as high, and beyond about 19 per cent as extreme. Those bands are conventions from published setup guides, not rules, and different makers draw the lines in slightly different places.
The useful thing to understand is what the bands describe rather than what they prescribe. A forward balance point tends to make an arrow recover from paradox and settle onto its line sooner, which shows up as tighter groups at longer distances and more forgiveness of a slightly imperfect release. It also increases drag-induced deceleration slightly and steepens the trajectory, because you have added mass at the front without adding energy. Nothing about a higher number is automatically better; it is a trade you make deliberately, and the right answer depends on the distance you shoot and what the arrow has to do when it arrives.
Why Arrow Length Is Measured to the Shaft, Not the Point
This one deserves its own section because it invalidates so many published FOC figures. The formula treats the arrow as a rod of length L with a balance point somewhere along it. The convention that came out of the archery trade defines L as nock throat to the end of the shaft, and every band described above was drawn against that convention. If you instead measure to the tip of a 100-grain field point, you have added roughly an inch to L and moved the reference midpoint half an inch forward, which shifts the reported FOC by a percentage point or more. Two archers comparing FOC numbers who measured differently are not comparing anything at all.
There is a second, subtler version of the same problem: measuring the balance point on a bare shaft and then reporting it as the finished arrow's FOC. Fletching, wrap and nock all sit behind the midpoint and pull the balance point rearward. A bare shaft with a point fitted will always read higher FOC than the same arrow once it is fletched. Always balance the arrow in the state you will actually shoot it.
FOC, Total Weight and Grains Per Pound Are Three Different Levers
Adding 50 grains to the point does three things at once: it raises FOC, it raises total arrow weight, and it raises grains per pound. Those are separate consequences and they do not all move in the same useful direction. FOC goes up, which may be what you wanted. Total weight goes up, which lowers launch speed and flattens nothing. Grains per pound goes up, which changes how much of the bow's stored energy the arrow absorbs. If your goal was purely a forward balance point, the same shift can be achieved instead by lightening the rear — a smaller nock, no wrap, shorter vanes — without adding mass at all.
The reverse also holds. Cutting an arrow shorter raises FOC even with no component change, because you have removed shaft length from behind the balance point as well as in front of it, and the point is now a larger fraction of a lighter arrow. This is why FOC and cut length cannot be chosen independently, and why arrow length is set by draw length and clearance first, with FOC adjusted afterwards. Our draw length calculator covers the measurement that sets that starting point.
Spine Is the Constraint FOC Has to Live Inside
Dynamic spine — how much the shaft flexes under the specific bow that launches it — is the variable that decides whether an arrow flies straight at all, and point weight is one of the main things that changes it. A heavier point makes a shaft behave weaker, because more mass at the front resists acceleration and forces the shaft to bend more. That is why you cannot simply keep adding point weight to chase a higher FOC number: past a certain point the shaft is no longer stiff enough for the bow, and the arrow leaves the string with an oscillation it never recovers from.
Shaft makers publish spine selection charts precisely because this interaction is not something to guess at. The chart takes draw weight, draw length and point weight together and returns a spine value. If a heavier point takes you outside the chart's cell, the correct move is a stiffer shaft, not a smaller point. The published equipment rules maintained by World Archery govern what is permitted in competition, and they are worth reading before building a set of arrows for a scored event.
Where the Number Stops Being Useful
FOC describes a static balance point. It says nothing about the arrow's stiffness, its straightness tolerance, its weight consistency across a dozen shafts, or how well the fletching stabilises it. Two arrows with identical FOC and identical mass can group very differently if one set is sorted for spine and weight and the other is not. FOC is also a poor predictor of anything at short distances, where the arrow simply does not have time for its recovery behaviour to matter much.
It is likewise not a substitute for shooting the arrows. Paper tuning, bare-shaft tuning and group testing at the distance you actually shoot will tell you things no percentage can. Treat FOC as a way to describe and repeat a setup you arrived at by testing, not as a specification to build towards on paper.
Arb Digital builds free calculators like this one as search-visible entry points for specialist retailers, then turns the traffic they earn into enquiries with content and technical SEO built around the terms your customers actually type.
SEO Services Talk to Arb DigitalCommon Mistakes to Avoid
- Measuring arrow length to the point tip. The convention is nock throat to the end of the shaft. Including the point inflates every FOC figure you calculate.
- Balancing a bare shaft. Fletching, wrap and nock all sit behind centre and pull the balance point back. Balance the arrow exactly as you will shoot it.
- Chasing a target percentage. Nothing in the published bands says a particular number is correct for a particular archer. FOC is a description of a setup, not a specification.
- Ignoring what point weight does to spine. A heavier point makes a shaft act weaker. Past the maker's chart, the fix is a stiffer shaft, not a lighter point.
- Forgetting the glue and the wrap. Adhesive, wraps and heavy nocks add real grains at the back. Weigh the finished arrow and reconcile it against the calculated total.
Related Free Tools From Arb Digital
Once the arrow is built, our arrow speed calculator estimates launch speed from the bow's published rating and the finished arrow weight, and the draw length calculator covers the measurement that sets your cut length in the first place. For the underlying physics, the kinetic energy calculator and the momentum calculator handle the general forms, and the projectile motion calculator shows how launch angle and height interact over distance. Browse the full free online tools hub for everything else.
Frequently Asked Questions
FOC stands for front of centre. It is the percentage of the arrow's length by which the balance point sits ahead of the physical midpoint. A 29-inch arrow balancing 2.9 inches ahead of its midpoint has an FOC of 10 per cent.
From the throat of the nock to the cut end of the shaft. The point is not included. Measuring to the tip of the point instead adds length and shifts the reference midpoint, which inflates the calculated percentage by roughly a point or more.
Published manufacturer literature describes bands rather than targets: under about 7 per cent is low, 7 to 12 per cent normal, 12 to 19 per cent high, and above roughly 19 per cent extreme. Those are descriptive conventions, and the right setup depends on your distance, equipment and testing rather than on a number.
Yes, adding weight at the front moves the balance point forward. It also raises total arrow weight and makes the shaft behave weaker in dynamic spine, so the change has three consequences, not one.
Always the finished arrow. Nock, wrap and fletching sit behind the midpoint and move the balance point rearward, so a bare shaft will read a higher FOC than the same arrow once it is built.
Yes. Reducing rear-end mass with a lighter nock, no wrap or shorter vanes moves the balance point forward without increasing the finished arrow weight, which keeps launch speed closer to where it was.
It is the finished arrow weight divided by the bow's peak draw weight. Manufacturers and organisations use it to describe how heavy an arrow is relative to the bow, and it is the figure minimum arrow weight guidance is usually written against.
Indirectly. Moving weight forward without adding energy raises total mass, which lowers launch speed and steepens the trajectory. The balance shift itself mainly affects how quickly the arrow recovers and stabilises after release.
This calculator reproduces published archery arithmetic for information only. Arrow spine, point weight and bow setup interact in ways a percentage cannot capture, and equipment should be selected and set up with a qualified bow technician using the shaft and bow manufacturer's own charts and instructions.
