Free Industrial Maintenance Calculator

Belt Drive Speed & Ratio Calculator

Calculate driven shaft RPM, speed ratio, belt velocity and belt length from driver and driven pulley diameters.

Belt Drive Speed & Ratio Calculator

Enter driver and driven pulley diameters and driver speed.

Driven RPM = Driver RPM × (Driver Ø ÷ Driven Ø). Belt length formula: 2C + π(D1+D2)/2 + (D2−D1)²/(4C).

Frequently Asked Questions

How do I calculate the driven shaft speed for a belt drive?

Driven RPM = Driver RPM × (Driver pulley diameter ÷ Driven pulley diameter). For example, a 1450 RPM motor with a 150 mm driver pulley driving a 300 mm driven pulley gives: 1450 × (150 ÷ 300) = 725 RPM output. Belt slip reduces actual output by 1–3%.

What is the recommended maximum belt speed for V-belts?

Classical V-belts should not exceed 25–30 m/s (1500–1800 m/min). Narrow V-belts (SPZ, SPA, SPB, SPC) can operate up to 35 m/s. Above these speeds, centrifugal force reduces effective belt tension and power capacity. The optimal range for most industrial drives is 10–22 m/s.

How do I find the correct V-belt replacement cross-section?

V-belt cross-sections (Z/SPZ, A/SPA, B/SPB, C/SPC) are selected based on the design power (kW) and speed of the faster shaft. Belt manufacturers provide selection charts. For replacement, match the cross-section markings printed on the old belt (e.g., "A40" means A-section, 40-inch pitch length).