An arrow build calculator helps bowhunters and archers optimize their arrow setup by calculating total arrow weight, Front of Center (FOC) percentage, kinetic energy, and momentum from individual components. Whether you're building a hunting arrow for whitetail or tuning target shafts, knowing these numbers ensures your arrows fly true and hit hard.
Preset Arrow Builds
Arrow Components
Grains per inch — check shaft specs
Cut length, nock groove to end of shaft
75-200 gr typical
15-50 gr typical
7-15 gr typical
6-12 gr per vane
5-10 gr if using wraps
IBO or chronographed speed
FOC Rating
--Kinetic Energy Rating
--Weight Breakdown
How to Use the Arrow Build Calculator
Building the perfect arrow starts with understanding how each component contributes to total weight, balance, and terminal performance. This free arrow build calculator lets you enter each component individually and instantly see how your choices affect FOC, kinetic energy, and momentum — the three numbers that matter most for bowhunting effectiveness.
Step 1: Enter Shaft Specifications
Start with your arrow shaft's grains-per-inch (GPI) rating and the cut length in inches. The GPI is listed on the manufacturer's spine chart. Multiply GPI by length to get the raw shaft weight. For example, an 8 GPI shaft cut to 28 inches produces a 224-grain shaft. Carbon shafts typically range from 6 to 12 GPI depending on spine and wall thickness.
Step 2: Add Front Components
Enter the weight of your point or broadhead (commonly 100 or 125 grains for hunting) and your insert weight (15-50 grains). These front-end components are the biggest factor in your arrow's FOC percentage. Heavier points push the balance point forward, increasing FOC and improving penetration. Many bowhunters add weight to the insert or use heavy brass inserts to boost FOC without changing broadheads.
Step 3: Add Rear Components
Enter the nock weight (7-15 grains), individual vane weight (6-12 grains each), and the number of vanes (3 or 4). If you use arrow wraps, add that weight too (5-10 grains). Rear components are generally light, but switching from 4 heavy feathers to 3 lightweight vanes can shave 20+ grains off the back end, which also improves FOC.
Step 4: Enter Bow Speed
Input your bow's arrow speed in feet per second (fps). This can be the IBO rating from the manufacturer or, ideally, a chronographed speed with your actual setup. The calculator uses this to compute kinetic energy and momentum. KE tells you how much energy the arrow delivers on impact, while momentum indicates the arrow's ability to push through bone and tissue for a clean pass-through.
Understanding Your Results
The calculator displays four key metrics: total arrow weight in grains, FOC percentage, kinetic energy in foot-pounds, and momentum in slug-feet per second. It also provides rating badges: FOC is categorized as low (under 10%), ideal (10-15%), high (15-20%), or extreme (over 20%). Kinetic energy is rated by game size: small game needs 25+ ft-lbs, medium game 40+, large game 50+, and dangerous game 65+. Use the preset builds as starting points and adjust components to dial in your ideal balance of speed, weight, and penetration for your specific hunting scenario.
Frequently Asked Questions
Is this arrow build calculator free?
Yes, this arrow build calculator is completely free with no signup, no account, and no limits. All calculations run locally in your browser, so you can plan arrow builds anytime.
Is my data safe and private?
Absolutely. Everything runs in your browser using JavaScript. No arrow build data or personal information is sent to any server. When you close the page, all data is gone.
What is FOC (Front of Center) and why does it matter?
FOC stands for Front of Center and measures how much of an arrow's weight is concentrated toward the front. Higher FOC improves arrow flight stability and penetration on game. Most bowhunters aim for 10-15% FOC for a good balance of accuracy and lethality.
How much kinetic energy do I need for deer hunting?
Most experts recommend at least 40 ft-lbs of kinetic energy for medium game like whitetail deer. For larger game like elk, aim for 50+ ft-lbs. For dangerous game such as bear or moose, 65+ ft-lbs is recommended for reliable penetration.
What is a good total arrow weight for hunting?
A general guideline is 6-8 grains per pound of draw weight for hunting. For a 70-lb bow, that means 420-560 grains total arrow weight. Heavier arrows penetrate better but fly slower, while lighter arrows are faster but may lack penetration on large game.
How do I calculate arrow shaft weight?
Multiply the shaft's grains per inch (GPI) rating by the arrow length in inches. For example, an 8 GPI shaft cut to 28 inches weighs 224 grains. GPI is listed on the shaft manufacturer's specifications and varies by material and spine rating.
Why does momentum matter for bowhunting?
Momentum measures an arrow's ability to push through resistance like hide, bone, and tissue. A heavier arrow at moderate speed often has more momentum than a light arrow at high speed. Many bowhunters prioritize momentum over raw kinetic energy for better penetration on tough-angled shots.
What is the difference between kinetic energy and momentum for arrows?
Kinetic energy measures the total energy an arrow carries and is proportional to velocity squared. Momentum is proportional to velocity and represents the arrow's ability to maintain penetration through resistance. Both matter: KE for initial impact and momentum for follow-through.