# What is my arrow speed?

Estimates the speed of an arrow in ft/s from the bow’s IBO rating, your draw length, draw weight, arrow weight and string weight, with its kinetic energy and momentum.

- Page: https://www.acalculator.org/sports/arrow-speed-calculator
- JSON spec: https://www.acalculator.org/sports/arrow-speed-calculator.json
- Version: d7ebf4b8cb4f

## Default answer

Example with the default inputs (IBO speed rating (ft/s) 330, Draw length (in) 28, Peak draw weight (lb) 60, Arrow weight (grains) 400, Weight on the string (grains) 0): Your arrow flies at about 276.7 ft/s with 68 ft·lbf of kinetic energy.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| ibo | IBO speed rating (ft/s) | The bow’s rated speed in feet per second, from its maker. |
| dl | Draw length (in) | Your draw length in inches. |
| dw | Peak draw weight (lb) | The bow’s peak draw weight in pounds, as you have it set. |
| aw | Arrow weight (grains) | The total weight of the arrow with its point, in grains. |
| sw | Weight on the string (grains) | Extra weight on the bowstring (peep sight, nock loop, silencers), in grains; 0 for none. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| fps | Arrow speed (ft/s) | The estimated speed of the arrow in feet per second. |
| mps | Arrow speed (m/s) | The same speed in metres per second. |
| energy | Kinetic energy (ft·lbf) | ½ m v², in foot-pounds. |
| joules | Kinetic energy (J) | ½ m v², in joules. |
| momentum | Momentum (slug·ft/s) | m v, in slug-feet per second (pound-force seconds). |
| momentumSi | Momentum (kg·m/s) | m v, in kilogram-metres per second. |
| grainsPerPound | Arrow grains per pound | Arrow weight ÷ draw weight. The IBO test arrow is 5 grains per pound. |

## Method

Speed (ft/s) = IBO + 10 × (draw length − 30) − (arrow weight − 5 × draw weight) ÷ 3 − string weight ÷ 3; KE = ½ m v²; momentum = m v.

## Assumptions

- The IBO rating is measured at 70 lb, a 30 in draw, a 350 grain arrow (5 grains per pound) and nothing on the string.
- The rules of thumb are linear; real bows differ, so a chronograph gives the true speed.
- Arrows lighter than 5 grains per pound of draw weight are outside the rules (and below the IBO test weight).

## Worked examples

1. ibo = 330, dl = 30, dw = 70, aw = 350, sw = 0 gives fps = 330, mps = 100.584, grainsPerPound = 5. Source: Sunrise Archery, Understanding Bow Speeds (IBO speed rating: 70 lb, 30 in draw, 350 grain arrow). https://sunrisearchery.com/resources/understanding-bow-speeds/.
2. ibo = 330, dl = 28, dw = 60, aw = 400, sw = 0 gives fps = 276.666667, energy = 67.973545, momentum = 0.491375. Source: N1 Outdoors, Arrow Speed Calculator (draw length ±10 ft/s per inch from 30 in; −1 ft/s per 3 grains of arrow weight above 5 × draw weight; −1 ft/s per 3 grains on the string). https://n1outdoors.com/arrow-speed-calculator/; Sunrise Archery, Understanding Bow Speeds (IBO speed rating: 70 lb, 30 in draw, 350 grain arrow). https://sunrisearchery.com/resources/understanding-bow-speeds/ (this setup shoots about 275 ft/s); NIST SP 811 (2008), Appendix B.8 (1 grain = 64.79891 mg; 1 ft = 0.3048 m; 1 lbf = 4.4482216152605 N). https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8.
3. ibo = 340, dl = 29, dw = 70, aw = 425, sw = 12 gives fps = 301, joules = 115.901632, energy = 85.484657. Source: N1 Outdoors, Arrow Speed Calculator (draw length ±10 ft/s per inch from 30 in; −1 ft/s per 3 grains of arrow weight above 5 × draw weight; −1 ft/s per 3 grains on the string). https://n1outdoors.com/arrow-speed-calculator/; NIST SP 811 (2008), Appendix B.8 (1 grain = 64.79891 mg; 1 ft = 0.3048 m; 1 lbf = 4.4482216152605 N). https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8.

## FAQ

### What is the IBO speed rating?

It is the speed a bow shoots under a standard test: 70 lb peak draw weight, 30 in draw length and a 350 grain arrow (5 grains per pound), with nothing on the string. Most setups are slower than the rating.

### How do I estimate my arrow speed?

Start from the IBO rating. Add or take away 10 ft/s for each inch of draw length above or below 30 in. Take away 1 ft/s for every 3 grains of arrow weight above 5 grains per pound of draw weight, and 1 ft/s for every 3 grains on the string.

### How fast is a 330 ft/s bow at 28 in and 60 lb?

With a 400 grain arrow: 330 − 2 × 10 − (400 − 5 × 60) ÷ 3 = 276.7 ft/s. Sunrise Archery gives about 275 ft/s for the same setup.

### How is arrow kinetic energy worked out?

Kinetic energy is ½ m v². With m in kilograms (1 grain = 64.79891 mg) and v in m/s it comes in joules; divide by 1.3558 for foot-pounds. A 400 grain arrow at 276.7 ft/s carries about 68 ft·lbf.

### Why can my arrow not be lighter than 5 grains per pound?

The IBO test arrow is 5 grains per pound of draw weight, and the speed rules only cover heavier arrows. Bow makers warn against arrows below their minimum weight, because a light arrow leaves much of the energy in the bow.

### How accurate is this estimate?

The rules are averages. Brace height, cam design, let-off and string accessories also change the speed, so a chronograph gives your true speed. Use the estimate to compare setups.

## Sources

- Sunrise Archery & Outdoors, Understanding Bow Speeds (IBO speed rating: 70 lb, 30 in draw, 350 grain arrow; rough changes per inch of draw and per grains of arrow weight; a 330 ft/s bow at 60 lb, 28 in and 400 gr shoots about 275 ft/s). https://sunrisearchery.com/resources/understanding-bow-speeds/ (retrieved 2026-10-02)
- N1 Outdoors, Arrow Speed Calculator (each inch of draw length under 30 in takes 10 ft/s from the IBO value, each inch over adds 10; every 3 grains of arrow weight above draw weight × 5 takes 1 ft/s; every 3 grains on the string takes 1 ft/s). https://n1outdoors.com/arrow-speed-calculator/ (retrieved 2026-10-02)
- NIST SP 811 (2008), Appendix B.8, Factors for Units Listed Alphabetically (1 grain = 6.479891 × 10⁻⁵ kg; 1 ft = 0.3048 m; 1 lbf = 4.4482216152605 N). https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8 (retrieved 2026-10-02)