Prop Pitch Calculator

Find the theoretical speed from propeller pitch and rpm.

Theoretical speed 79.545

Theoretical speed (kn) 69.123

Formula: speed = pitch × rpm × 60 ÷ 63360

Step-by-step with your numbers:

1. Values used:

2. Propeller pitch = 21

3. Propeller RPM = 4,000 rpm

5. Theoretical speed = 79.545

6. Theoretical speed = 69.123kn

Did we solve your problem today?

Propeller pitch is how far it would travel in one turn through a solid — like a screw.

The math behind it

Theoretical speed = pitch × rpm, converted to mph. Real speed is lower because of prop slip.

21" pitch at 4000 rpm → about 79.5 mph theoretical.

Why is real speed lower?

Water (or air) yields, causing slip — usually 10–20%.