Propeller Pitch Calculator
Use our propeller pitch calculator to calculate prop pitch (in) from boat speed, gear ratio, engine RPM, and propeller slip. Includes what propeller pitch is, how propeller pitch works, and the propeller pitch formula used for boats.
What Is Propeller Pitch?
Propeller pitch is the theoretical distance a prop would move forward in one full revolution, measured in inches. For example, a 21-inch pitch prop is designed to advance about 21 inches per revolution in a perfect, no-slip scenario.
In the real world, propeller slip reduces actual forward movement because water is not a solid. Slip is expressed as a percentage and depends on hull design, load, trim, and prop selection.
This propeller pitch calculator estimates pitch from boat speed (mph), engine/crankcase speed (RPM), gear ratio, and slip (%).
Propeller Pitch Formula
Boat speed relates to prop RPM and pitch, adjusted for slip. This calculator solves for pitch.
Gear ratio is entered as X:1, meaning the engine turns X times per 1 prop revolution.
1056 converts inches/min to miles/hour (12 in/ft × 5280 ft/mi ÷ 60 min/hr). Slip is entered as a decimal (example: 10% = 0.10).
Use slip as a percent converted to a decimal (Slip% ÷ 100).
Higher slip or lower RPM requires more pitch to reach the same speed.
How to Calculate Propeller Pitch
- 1
Enter boat speed (mph).
- 2
Enter gear ratio (X:1).
- 3
Enter engine/crankcase speed (RPM).
- 4
Enter propeller slip (%).
Frequently Asked Questions
Pitch is the theoretical forward travel per prop revolution. Higher pitch can increase potential top speed but may reduce acceleration or raise engine load, depending on the boat and motor.
You can read it from markings on the prop, measure it physically, or estimate it from speed, RPM, gear ratio, and slip using the pitch formula.
Many props have pitch stamped on the hub. Physical measurement is possible but more involved because pitch relates to blade angle and helix geometry.
Slip is the percentage difference between theoretical travel (based on pitch and RPM) and actual travel through water. It accounts for real-world losses and water behavior.
Pitch angle refers to the blade angle relative to the plane of rotation. Pitch (inches) is derived from that geometry as the theoretical travel per revolution.