Bow makers rate bows by IBO speed: the speed of a 350-grain arrow (5 grains per pound) shot with a 30-inch draw and a 70-lb draw weight. Your real setup is almost always slower, and knowing the actual speed matters for sight settings, trajectory and the energy delivered to the target.
How to use the Arrow Speed Calculator
- IBO speed rating
- Draw length
- Peak draw weight
- Arrow weight
- Additional weight on the string
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Each inch of draw length shorter than 30 in costs about 10 ft/s, every 3 grains on the string (peep sight, silencers) costs about 1 ft/s, and every 3 grains of arrow weight above 5 grains per pound of draw weight costs another 1 ft/s. Kinetic energy and momentum follow from the arrow mass and speed.
Inputs explained
| Field | What to enter |
|---|---|
| IBO speed rating | Units: ft/s, m/s, mph, km/h |
| Draw length | Units: in, mm, cm, ft, m |
| Peak draw weight | Units: lb, kg, t, US ton |
| Arrow weight | Units: gr, g, kg, oz |
| Additional weight on the string | Units: gr, g, kg, oz |
What each result means
- Estimated arrow speed = ([IBO speed rating]÷0.3048 + ([L] – 30)×10 – [W]÷3 + min(0, -([A] – 5×[P])÷3))×0.3048
- Kinetic energy = [Arrow weight]×[Estimated arrow speed]^2÷2
- Momentum = [Arrow weight]×[Estimated arrow speed]
Example values
How the main result changes when IBO speed rating changes and everything else stays at the example values above:
| IBO speed rating (ft/s) | Estimated arrow speed (ft/s) |
|---|---|
| 165 | 118.33 |
| 247.5 | 200.83 |
| 330 | 283.33 |
| 412.5 | 365.83 |
| 495 | 448.33 |
| 660 | 613.33 |
Formula
v = IBO + (L − 30) × 10 − W/3 + min(0, −(A − 5P)/3)
KE = A × v² / 450,240 (ft·lbf, A in grains, v in ft/s)
Worked example
Inputs — IBO speed rating: 330 ft/s; Draw length: 29 in; Peak draw weight: 60 lb; Arrow weight: 400 gr; Additional weight on the string: 10 gr.
Results — Estimated arrow speed = 283.33 ft/s; Kinetic energy = 96.65 J; Momentum = 2.2384 kg·m/s.
Key terms
- IBO speed
- The International Bowhunting Organization standard speed rating.
- Grain
- A unit of mass: 1 grain = 64.79891 mg.
Frequently asked questions
What is IBO speed?
A standard test speed measured with a 70-lb, 30-inch draw bow and a 350-grain arrow.
How much speed does a heavier arrow cost?
About 1 ft/s for every 3 grains above 5 grains per pound of draw weight.
Is a faster arrow always better?
Faster arrows shoot flatter, but heavier arrows carry more momentum and penetrate better.
How much kinetic energy do I need for hunting?
Guidelines vary; many hunters aim for at least 40–65 ft·lbf for deer-sized game.