Prop Pitch Calculator

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

How the Math Works

The Prop Pitch Calculator uses the formula speed = (pitch × rpm × 60) ÷ 63360 to convert theoretical propeller movement into miles per hour. Pitch (in inches) represents how far the propeller moves forward in one revolution. Multiplying by RPM (revolutions per minute) gives inches per minute, then multiplying by 60 converts this to inches per hour. Finally, dividing by 63,360 (the number of inches in a mile) yields the speed in miles per hour. This calculation assumes no slippage, providing an idealized maximum speed.

Practical Applications

To use this calculator, measure the propeller's pitch (distance traveled in one revolution) and note the engine's RPM at a given throttle setting. Input these values into the formula to estimate the boat's theoretical speed. For example, a propeller with a 20-inch pitch spinning at 1,000 RPM would calculate to approximately 18.94 mph. This helps compare propeller efficiency, diagnose engine performance issues, or select optimal propeller specifications for specific watercraft applications.

Day-to-Day Use

This calculation empowers boaters to quickly estimate their vessel's potential speed without costly sea trials. By comparing theoretical and actual speeds, users can identify mechanical problems like propeller damage or engine inefficiencies. It also aids in everyday decisions—such as choosing the right propeller pitch for fuel efficiency or determining if a boat's performance meets expectations before heading out on the water.

Worked example

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

FAQ