Pulley speed calculator
Handy when sizing a pulley for a fan, compressor or lathe to reach a target speed. Enter both diameters and the driver speed.
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How to use it
- Enter driver pulley diameter, driven pulley diameter and driver pulley speed.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Driven speed = driver speed × driver diameter ÷ driven diameter. Belt speed (m/s) = π × driver diameter (mm) × driver rpm ÷ 60000.
Example
Inputs: Driver pulley diameter = 100 mm, Driven pulley diameter = 200 mm, Driver pulley speed = 1,450 rpm. Result: Driven pulley speed: 725 rpm; Pulley ratio: 2 : 1; Belt speed: 7.592 m/s.
Limits and caveats
- Ignores belt slip, so the real driven speed is slightly lower.
- For V belts, use the pitch (datum) diameter, not the outside diameter.
Questions about this tool
How do I double the machine speed?
Make the driven pulley half the diameter of the driver pulley and its speed doubles.
Which diameter do I measure on a V belt pulley?
The pitch diameter, where the middle of the belt sits. It is smaller than the outside diameter and is listed in the pulley catalogue.
Why does belt speed matter?
Each belt type has a maximum speed set by the maker, and speed affects how much power the belt can carry.