0 A DBB & OGH Joint Project Calculator



This calculator is based on the AMO-Standard F.O.C. balance formula is: %FOC = (100x(B-L/2))/L
L (Length)

B (Balance Point
Length )


FOC Classes Per Dr. Ashby

Normal FOC: Up to 12%
Target & 3D Shooting
High FOC: 12% – 18%
For small to large game
Rabbit, turkey, deer, elk, etc.
Extreme FOC: 19% – 30%
Large to extremely large game
Elk, black bear, wild boar, grizzly bear, etc.
Ultra-Extreme FOC: above 30%
Cape buffalo, elephant, etc.
About This Calculator
How much FOC you have is strictly up to you.
As soon as the arrow leaves the bow positive acceleration has stopped and negative acceleration starts. Because the arrow is moving it has kinetic energy, momentum, and inertia. All are important in getting the arrow to the target. But only two will get the arrow through the target. Here are a few questions you need to ask yourself
  1. Do you want the nock to be pushing the arrow through the air, or do you what the point to be pulling the arrow through the air?
  2. How much penetration do you want? Momentum is made up of both mass and velocity (weight and speed) of the arrow. When mass provides the greater part of the equation the greater chance of more penetration.
  3. Where do you want the majority of the weight of the arrow, the front half or the back half? Even if the arrow's weight is evenly distributed so that the balance point is dead in the center of the shaft the arrow is not going to fly very well.

How To Calculate FOC

To find the FOC of an arrow, install (points,vanes, inserts, nock).

  1. Enter The Arrow Length (L) This is the overall length of the arrow measured from the throat of the nock* to the end of the shaft.

  2. Enter The Balance Point Length (B)
    This is where the arrow balances perfectly. Measure from the throat of the nock*.

* Throat of the nock - The throat of the nock is where the string makes contact with that arrow. See the image above.

An alternate method of measuring the arrows length

  1. Measure the complete length from the tip of the point to the end of the nock for value (L)

  2. Measure from the balance point to the end of the nock for value (B)
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