Pulley RPM Calculator
Driven pulley speed, ratio and belt length.
Enter your values
ⓘ Live results
Results
- Driven pulley RPM
- 3,500 rpm
- Drive ratio
- 0.5 : 1
- Belt speed
- 2,749 ft/min
- Belt length needed
- 50.26 in
Quick answer
Driven RPM = drive RPM × drive diameter ÷ driven diameter, because both pulleys share the same belt surface speed.
RPM₂ = RPM₁ × D₁ ÷ D₂
How to use the Pulley RPM Calculator
- 1Enter the drive pulley diameter and its RPM.
- 2Enter the driven pulley diameter.
- 3Add the centre distance for a belt length estimate.
Worked example
Using the values the calculator loads with:
Inputs
- Drive pulley diameter6 in
- Drive pulley RPM1750 rpm
- Driven pulley diameter3 in
- Centre distance18 in
Results
- Driven pulley RPM3,500 rpm
- Drive ratio0.5 : 1
- Belt speed2,749 ft/min
- Belt length needed50.26 in
Frequently asked questions
Does a smaller driven pulley spin faster?
Yes — halving the driven diameter doubles its RPM but halves the available torque.
What belt length do I need?
Use the calculated length, then round up to the nearest stock belt and check the tensioner range.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.