Arrow weight and estimated FOC calculator
Estimate arrow weight, FOC, kinetic energy, and momentum from component weights, shaft length, and measured speed.
Enter shaft grains per inch, shaft length, point weight, insert weight, rear component weight, and measured launch speed.
The calculator returns total grains, estimated FOC, kinetic energy, and momentum.
Where the formulas come from
The app multiplies shaft grains per inch by shaft length, then adds component weights.
Kinetic energy is weight times speed squared divided by 450240. Momentum is weight times speed divided by 225218.
Weight uses grains. Speed uses feet per second.
The FOC model places rear weight at 1.75 inches from the nock throat and shaft weight at half the shaft length.
It places insert weight at the greater of shaft length minus 0.45 inches or 85 percent of shaft length.
It places point weight 0.55 inches beyond shaft length. These positions are model assumptions from the app code.
Measure the real balance point to confirm estimated FOC. Use a chronograph to measure launch speed.