Marine Gearbox Ratio Calculator
Calculate shaft RPM from engine RPM and your reduction ratio.
A QUICK WALKTHROUGH
How to use this tool
- Enter engine RPM and the established reduction ratio.
- Use the convention engine revolutions divided by shaft revolutions; the ratio must be at least 1.
- Calculate shaft RPM, then copy or download the report.
Formula and units
Shaft RPM = engine RPM ÷ reduction ratio (engine revolutions : shaft revolutions).
Scope
This is a speed ratio calculation, with no torque, efficiency, power, propeller suitability or gearbox recommendation. Confirm the ratio convention from your equipment information.
Local processing
Inputs stay in your browser. The report includes inputs, formulas and scope.
GOOD TO KNOW
Common questions
Does the result calculate torque or efficiency?
No. It only divides rotational speed by the supplied reduction ratio.