Pulley speed and belt speed calculator

Driven pulley rpm, speed ratio and belt speed from diameters.

Calculating…

How it's calculated

n2 = n1 × D1 ÷ D2 Belt speed = π × D1 × n1 ÷ 60 000 (m/s, D in mm)

Speeds are in inverse proportion to pulley diameters. Use pitch diameters for V-belt and timing-belt drives; outside diameters give a small error.

V-belts typically slip 1–3%, so the measured driven speed will be slightly lower than calculated.