Pulley RPM Calculator
Driven pulley speed, ratio and belt length.
Enter your values
Results update instantly as you type — no submit needed.
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
At a glance
| What it does | Driven pulley speed, ratio and belt length. |
|---|---|
| Category | Engineering |
| Inputs needed | Drive pulley diameter, Drive pulley RPM, Driven pulley diameter, Centre distance |
| Main output | Driven pulley RPM |
| Formula | RPM₂ = RPM₁ × D₁ ÷ D₂ |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Drive pulley diameter(in)
- Enter the drive pulley diameter you are working with.
- Drive pulley RPM(rpm)
- Enter the drive pulley rpm you are working with.
- Driven pulley diameter(in)
- Enter the driven pulley diameter you are working with.
- Centre distance(in)
- Enter the centre distance you are working with.
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.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.