⚖️ FOC (Front of Center) Calculator

Balance your arrow on an edge to find its balance point measured from the nock end, then enter it here along with total arrow length to calculate FOC.

Arrow length (in)

Balance point from nock (in)

How front of centre is worked out

FOC is how far the balance point sits ahead of the arrow's midpoint, written as a percentage of the whole arrow:

FOC % = (balance point − length ÷ 2) ÷ length × 100

The defaults are a 29 in arrow balancing 16.5 in from the nock. Centre is 14.50 in, so the balance sits 2 in forward: 2 ÷ 29 = 6.9%. Move it to 17.5 in and you get 3 ÷ 29 = 10.3%. A balance point behind centre returns a negative percentage.

Measuring it the same way twice

Measure both figures from the nock throat. The usual convention takes length from the throat of the nock groove to the end of the shaft, with the point excluded. Include a broadhead in one measurement and not the other and the percentage is meaningless.
Point weight is the main lever. A heavier point or insert pushes the balance forward and lifts FOC — and weakens dynamic spine at the same time, so re-read the spine chart after any point change.

The page shows 7-15% as a common range; treat that as context, not a target, because FOC trades forgiveness against trajectory and the right figure depends on the shot distances you actually take. One quirk to know: clear the length box and the code substitutes 1 in, which prints an absurd percentage rather than an error.

Frequently asked questions

What is a good FOC for a hunting arrow?

There is no single number. The 7-15% shown on the page covers most target and hunting builds; higher FOC tends to steady broadhead flight and costs trajectory, since the extra weight is nearly always at the point. Chase clean arrow flight first and read the FOC off the result.

How do I find an arrow's balance point?

Build the arrow completely — point, insert, nock and vanes — then lay it across a ruler edge and slide it until it stays level. Mark that spot and measure back to the throat of the nock.

Does adding point weight change the spine?

Yes. Weight at the front makes the shaft behave weaker at the shot, so going from a 100 to a 150 grain point can push you a spine step stiffer. Check the shaft maker's chart before committing to a dozen.