Pulley & Belt Drive Calculator

Find the driven speed, ratio and belt speed of a pulley drive from an electric motor.

Driver speed n₁ (rpm)

Driver pulley Ø d₁ (mm)

Driven pulley Ø d₂ (mm)

Driven speed n₂: — rpm

Ratio: —

Belt speed: — m/s

n₁·d₁ = n₂·d₂ · v = π·d₁·n₁ / 60000

How it works

The driven speed is inversely proportional to pulley diameter: n₂ = n₁ · d₁ / d₂. A larger driven pulley reduces speed and increases torque. Choose the motor speed/power accordingly — browse our power & speed range. Related: gearbox output · motor calculator.

Frequently asked questions

How do I calculate driven pulley speed?

n₂ = n₁ · d₁ / d₂. For 1450 rpm with d₁=100 mm and d₂=250 mm, n₂ ≈ 580 rpm.

What is the drive ratio?

Ratio = d₂ / d₁ (= n₁ / n₂). A ratio above 1 reduces speed and increases torque.

What belt speed is acceptable?

V-belts typically run up to ~25–30 m/s; check the belt and pulley manufacturer limits.