Arrow Speed Calculator
Estimate what your bow actually shoots. Enter the IBO/ATA speed rating (fps), your draw length (inches), draw weight (lb), total arrow weight (grains), and any weight added to the string — you get real-world arrow speed in fps and m/s, kinetic energy in ft-lb, and momentum.
Example: with IBO / ATA speed rating (fps) 320 · Your draw length (inches) 29 · Your draw weight (lb) 70 · Total arrow weight (grains) 420 · Weight added to string — peep, loop (grains) 15 → Estimated arrow speed: 282 fps (86 m/s).
- Kinetic energy74.0 ft-lb — heaviest game class (65+ ft-lb)
- Momentum0.525 slug·ft/s
- Arrow weight check6.00 grains per pound of draw weight — above the 5 gr/lb minimum
Computed by the calculator below using its default values. Change any input to see your own numbers.
Starts from the IBO standard (70 lb draw, 30" draw length, 350 gr arrow) and applies the shop rule-of-thumb corrections: ±10 fps per inch of draw, ±2 fps per pound of draw weight, 1 fps per 3 gr of extra arrow or string weight.
Why your bow doesn't shoot its IBO number
IBO/ATA ratings are measured under ideal lab conditions: a 70 lb bow at 30 inches of draw launching a bare 350-grain arrow — 5 grains per pound — from a naked string. Almost nobody hunts that setup. Shorter draws store less energy, heavier arrows soak up the same energy at lower speed, and every peep sight and D-loop adds moving mass to the string. Stack typical real-world choices and a '320 fps' bow commonly delivers 270–290 fps.
This tool applies the corrections pro shops use: subtract about 10 fps per inch of draw under 30, 2 fps per pound of draw weight under 70, and 1 fps for every 3 grains of arrow or string weight beyond the standard. It is a convention, not physics from first principles — expect the estimate to land within roughly 5–8 fps of a chronograph.
Speed is only half the hunting story
Flat trajectory sells bows, but penetration kills cleanly, and that is kinetic energy and momentum. KE = arrow weight × speed² ÷ 450,240 gives ft-lb; the widely used Easton-style bands run under 25 ft-lb for small game, 25–41 for deer-class animals, 42–65 for elk, and 65+ for the heaviest game. A heavier arrow leaves slower but usually carries more momentum and drives deeper. Verify with a chronograph before a hunt — and never drop below 5 grains per pound of draw weight, which stresses the bow like a dry fire and voids most warranties.
How it’s calculated
Speed = IBO + 10×(draw length − 30) − 2×(70 − draw weight) − (arrow weight − 5×draw weight)/3 − string weight/3, all in fps, inches, pounds, and grains. This is the standard archery-industry rule-of-thumb correction to the IBO/ATA test standard (70 lb, 30", 350 gr). KE (ft-lb) = arrow weight (gr) × v² / 450,240; momentum (slug·ft/s) = weight × v / 225,218 (i.e., grains→pounds ÷7,000, then ÷g = 32.174 ft/s²). 1 fps = 0.3048 m/s.
A rule-of-thumb estimator, not a ballistics model — cam design, arrow spine, and release style move real chronograph numbers by several fps, and the game-class bands are conventional guidance, not guarantees.
Kinetic energy guidance for bowhunting
| KE (ft-lb) | Commonly rated for |
|---|---|
| Under 25 | Small game — rabbit, squirrel |
| 25 – 41 | Medium game — deer, antelope |
| 42 – 65 | Large game — elk, black bear, wild boar |
| 65 and up | Heaviest game — moose, grizzly, cape buffalo |
Easton bowhunting field-chart bands, as widely republished by state wildlife agencies; check your state's legal minimum draw weight/KE.
Common mistakes
- Entering the arrow's shaft weight instead of total weight — field point or broadhead, insert, nock, and fletching all count.
- Ignoring string accessories: a 20-grain peep-plus-loop quietly costs about 7 fps.
- Treating the IBO number as your speed when your draw is 27.5 inches — that alone is roughly a 25 fps haircut.
- Chasing speed below 5 grains per pound of draw weight, which most manufacturers treat as a warranty-voiding dry-fire risk.
Frequently asked questions
What formula does this arrow speed calculator use?
Speed = IBO + 10×(draw length − 30) − 2×(70 − draw weight) − (arrow weight − 5×draw weight)/3 − string weight/3. It adjusts the IBO lab standard for your setup using the accepted shop rule of thumb.
How accurate is the estimate?
Usually within 5–8 fps of a chronograph for a well-tuned modern compound. Cam aggressiveness, string materials, and release style cause the spread — treat the number as a planning figure and verify before hunting.
How do I calculate arrow kinetic energy?
KE (ft-lb) = arrow weight in grains × speed in fps squared ÷ 450,240. A 420-grain arrow at 282 fps carries about 74 ft-lb — comfortably in the large-game band.
Does a heavier arrow ruin my speed?
It trades speed for penetration: about 1 fps lost per 3 extra grains. Because KE depends on v² but momentum on v, heavier arrows typically lose a little KE and gain momentum — many hunters accept 15 fps for a quieter bow and deeper-driving arrow.
Is IBO the same as ATA speed?
They are near-identical standards (350 gr arrow, 70 lb, 30" draw); ATA specifies the test more tightly. Manufacturers use the labels loosely, and either works as this calculator's starting number.