Pulley and Belt Calculator

How to calculate pulley speed and belt length

1. Enter the diameters of the driving and driven pulleys.
2. Enter the driving speed in RPM.
3. Enter the distance between the pulley centers to get the belt length.

Frequently asked questions

Which belt length formula is used?

The open belt formula: L = 2C + π(D + d) / 2 + (D − d)² / 4C, where C is the center distance.

How is the driven speed worked out?

Driving speed × driving diameter / driven diameter. A 100 mm pulley at 1,500 RPM turns a 200 mm pulley at 750 RPM.

Does belt slip matter?

V-belts slip slightly, so the real speed is a little lower than calculated. Toothed timing belts do not slip.