Pulley RPM Calculator
Driven pulley speed, ratio and belt length.
Enter your values
Enter the drive pulley diameter in in.
Enter the drive pulley rpm in rpm.
Enter the driven pulley diameter in in.
Enter the centre distance in in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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 in in.
- Drive pulley RPM(rpm)
- Enter the drive pulley rpm in rpm.
- Driven pulley diameter(in)
- Enter the driven pulley diameter in in.
- Centre distance(in)
- Enter the centre distance in in.
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.
What do I need to enter into the Pulley RPM Calculator?
Just 4 values: drive pulley diameter, drive pulley rpm, driven pulley diameter, centre distance. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Pulley RPM Calculator work out the answer?
Driven RPM = drive RPM × drive diameter ÷ driven diameter, because both pulleys share the same belt surface speed. It applies the formula RPM₂ = RPM₁ × D₁ ÷ D₂ and shows the working so you can check each step by hand.
Is the Pulley RPM Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.