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Pulley Speed Calculator

Find the output speed of a belt-and-pulley drive.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

In a belt-and-pulley drive, the belt moves at the same linear speed on both pulleys, which forces N₂ = N₁ × (D₁ / D₂) — the driven pulley's RPM equals the drive RPM times the ratio of the drive pulley's diameter to the driven pulley's diameter. A smaller driven pulley spins faster than the drive pulley; a larger one spins slower, trading speed for torque exactly the way gears do.

Mechanics and machine designers use this relationship constantly when sizing pulleys for a target output speed — automotive alternator and accessory drives, HVAC fan and blower belts, and workshop lathes and drill presses with step-cone pulleys all rely on this same diameter ratio to hit the RPM a motor or tool needs. Enter the drive RPM and both pulley diameters to find the driven pulley's speed.

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