Propeller Size Calculator 🔩

Calculate the ideal propeller pitch and estimated diameter for your boat. Enter desired speed, engine RPM, and gear ratio.

How to Use the Propeller Size Calculator

Enter desired cruising speed (knots), engine horsepower (HP), engine WOT RPM, gear ratio, and typical slip %. The calculator uses Dave Gerr's formula to recommend propeller pitch and estimate diameter.

Slip is the difference between theoretical and actual speed. Planing hulls: 10–15%. Displacement hulls: 15–20%.

Always verify prop selection with a certified marine mechanic. After fitting, confirm engine WOT RPM is within the manufacturer's recommended range.