RC Boat Speed Calculator
Estimate the theoretical pitch speed of an RC boat propeller from propeller RPM and pitch.
Propeller
Enter propeller RPM, not motor RPM. If the boat has a gearbox, divide motor RPM by the gear ratio first.
Speed unit
Result
Theoretical pitch speed
26.5mph
(42.7 km/h)
Propeller RPM
20000RPM
Theoretical pitch speed — real boat speed is lower because of slip, drag and load.
Formula
- 1.
Pitch Speed (mph) = Propeller RPM × Pitch (inches) / 1056 - 2.
km/h = mph × 1.609344
Worked example
- 1.Inputs: 20,000 RPM propeller, 1.4 inch pitch.
- 2.Propeller advance = 20,000 × 1.4 = 28,000 inches per minute.
- 3.Pitch speed = 28,000 / 1056 ≈ 26.5 mph ≈ 42.7 km/h.
Assumptions and limits
- Real boat speed is lower than pitch speed because of propeller slip, hull drag, load, voltage sag and water conditions.
- No universal slip percentage is applied — different hulls slip differently.
- This is a pitch-speed estimate only; it does not predict GPS-measured speed.
Related tools
Guides and concepts
FAQ
Why is my GPS speed lower than the pitch speed?
Propellers never advance their full pitch per revolution — slip, drag and load all take a cut. Pitch speed is the theoretical ceiling.
My motor runs at 30,000 RPM through a 2:1 gearbox — what do I enter?
Enter the propeller RPM, not the motor RPM: 30,000 / 2 = 15,000 RPM.
Assumptions
- Propeller RPM is used — if you only know motor RPM and the boat has a gearbox, divide motor RPM by the gear ratio first.
- Direct drive is assumed; slip is not applied.
- Result is a theoretical figure, not a measured boat speed.