Belts & Pulleys
Pulley Diameter Calculator
Enter the driver diameter, driver RPM, and desired driven RPM to estimate the required driven pulley diameter.
Inputs
Formula
Required driven diameter
Worked example
Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.
Inputs
- Driver pulley diameter
- 100 mm
- Driver speed
- 1,750 rpm
- Target driven speed
- 700 rpm
Result
- Required driven diameter
- 250 mm
Related calculators
Continue your workflow with a related calculation.
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Pulley RPM Calculator
Calculate driven pulley RPM from driver RPM and pulley diameters.
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Pulley Ratio Calculator
Calculate belt-drive speed ratio from driver and driven pulley diameters.
Belts & Pulleys
Belt Length Calculator
Calculate approximate open-belt length from pulley diameters and center distance, with metric and imperial results.
Frequently asked questions
Should I use pitch diameter or outside diameter?
Use the diameter convention appropriate to the belt system. For precision work, use pitch diameters consistently.
Will the calculated size give the exact target RPM?
It gives the ideal ratio. Available pulley sizes and belt slip can shift the real operating speed.