Pulley Belt Length Calculator

Find the belt length needed for a two-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

This calculator finds the length of an open (crossed-free) belt running between two pulleys of different or equal diameter: L = 2C + π(D+d)/2 + (D−d)²/(4C), where D and d are the pulley diameters and C is the centre-to-centre distance. The formula accounts for the straight spans on each side plus the wrap around each pulley.

Mechanical engineers, machinists, and maintenance technicians use it when designing or replacing a belt drive on a conveyor, motor, lathe, or fan, so they order a belt of the correct length instead of guessing and re-measuring. Enter both pulley diameters and the centre distance to get the required belt length.

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