Pulley and belt drive calculator

Calculate ideal driven RPM, pitch-line speed and geometric open-belt length from pitch diameters and center distance.

Dimension units

Changing units reinterprets the entered numbers.

Driver pitch diameter

Driven pitch diameter

Center distance

Driver speed

RPM

Measured driven speed

RPM

Optional. Compares measured speed with the ideal no-slip result.

Use effective pitch diameters from the actual belt/pulley specifications. Outside diameter can differ from pitch diameter.

Ideal driven speed

750RPM

Geometric belt length: 1476.2431 mm
Belt pitch-line speed: 7.854 m/s
Approximate belt length: 1476.2389 mm
Approximation difference: -0.004179 mm

The geometric length describes an ideal pitch line with no stretch or sag. Check the actual belt specification before choosing a part.

Pitch diameter and an open belt path

Under the no-slip model, driven RPM equals driver RPM multiplied by driver pitch diameter divided by driven pitch diameter. A 100 mm driver at 1,500 RPM turns a 200 mm driven pulley at 750 RPM.

The belt length adds the two straight tangent spans and the arcs around both pulleys. The approximate formula is useful for a quick check, and this tool reports its difference from the geometric model. Neither calculation accounts for tension, power rating, idlers, stretch or stock belt sizes.

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