Belt Length Calculator

This works out the length of a belt running over two pulleys from the two diameters and the distance between the shafts, using the exact tangent and arc geometry rather than the usual approximation. It returns the belt length, the wrap angle on each pulley, the straight span between them and the speed ratio, and it draws the drive to scale. A second mode goes the other way and finds the centre distance that fits a belt you already have. Open and crossed arrangements are both handled, and the catalogue approximation is shown beside the exact figure with its error.

Calculator Type

Units

Two pulley diameters and the distance between their shafts. Measure diameters on the pitch line, not the outer edge of the flange.

First Pulley Diameter (in) *

Second Pulley Diameter (in) *

Order does not matter; the larger of the two is treated as the driver pulley.

Centre Distance (shaft to shaft) *

Belt Arrangement

Widget