Belt & Pulley Calculator

Driven-pulley RPM, speed ratio, open-belt length and belt speed from the two pulley diameters, the drive speed and the centre distance.

Drive

Driver pulley Ø (D₁) mm

Driver speed (N₁) rpm

Driven pulley Ø (D₂) mm

Centre distance (C) mm

Results

Driven speed (N₂)—

Speed ratio—

Belt length (open)—

Belt speed—

N₂ = N₁ × D₁ / D₂. Open-belt length ≈ 2C + π(D₁+D₂)/2 + (D₂−D₁)²/4C. Belt speed = π·D₁·N₁. Keep belt speed within the belt's rating (often ≲ 25–30 m/s for V-belts) and round belt length to the nearest stock size.