Physics

Arrow Speed Calculator

Estimate arrow speed from bow IBO rating and setup.

Bow IBO speed (fps)

Draw length

Draw weight

Arrow weight (gr)

Calculated Output

Estimated speed (fps) 283.33

Formula: ≈ IBO + 10·(DL−30) + 2·(DW−70) − (gr−350)/3

Step-by-Step Breakdown

1. Values used:

2. Bow IBO speed = 320 fps

3. Draw length = 29

4. Draw weight = 65

5. Arrow weight = 400 gr

7. Estimated speed = 283.33fps

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The math behind it

Start from the IBO speed (rated at 30", 70 lb, 350 gr): add ~10 fps per inch of draw, ~2 fps per pound, and subtract ~1 fps per 3 grains over 350.

320 IBO, 29" draw, 65 lb, 400 gr → about 283 fps.

How accurate is it?

An estimate — real speed varies with bow efficiency; chronograph for exact values.