Free power-transmission utility

Belt drive helper

Estimate an open belt drive’s pitch length and driven speed from measured pulley sizes and shaft center distance. Use this to narrow a search, then confirm the exact belt and drive design with its manufacturer.

Driver pulley pitch diameter (in)Driven pulley pitch diameter (in)Center distance (in)Driver speed (RPM, optional)Measurement unit

Estimated belt pitch length67.02 inApproximate open-drive geometry

Estimated driven speed875 RPMAssumes no slip and pitch diameters

Enter pulley pitch diameters, not outside diameters. The estimate does not choose a belt section, account for belt stretch or tension, or confirm power capacity. Verify the exact belt length and drive design with the belt manufacturer.

How the estimate works

The approximate open-drive equation uses the larger and smaller pulley pitch diameters and the distance between shaft centers. Keep all three measurements in the same unit.

L ≈ 2C + π(D + d)/2 + (D − d)²/(4C)

Driven speed is estimated from the ratio of driver and driven pitch diameters. The calculation assumes no belt slip.

Driven RPM ≈ Driver RPM × Driver Pitch Diameter ÷ Driven Pitch Diameter

Before ordering a belt

Confirm the belt type and section, manufacturer’s length convention, pulley groove profile, power and speed rating, installation allowance, tension, and operating conditions. Catalog pitch, datum, effective, and outside lengths are not always interchangeable.

Review Gates belt-drive calculators and manufacturer guidance ↗

Looking for a documented part?

Search the replacement catalog.

Use the exact manufacturer and belt designation to find verified product records.

Need gearbox output speed instead? Use the gear ratio calculator →