Work out pulley speed ratio instantly with clear inputs, formula shown and shareable results.
Belt drives conserve surface speed, so the product of diameter and speed is the same at both pulleys: N2 = N1 x D1 / D2. Torque is multiplied by the inverse of the speed change, and belt speed in feet per minute is pi x diameter x rpm divided by 12.
Speed relation
N2 = N1 x D1 / D2; torque multiplier = D2 / D1
Belt speed
V fpm = pi x D in x rpm / 12
N2 = N1 x D1 / D2; torque multiplier = D2 / D1. Belt drives conserve surface speed, so the product of diameter and speed is the same at both pulleys: N2 = N1 x D1 / D2.
Yes. Classical V-belts are usually kept below about 5000 fpm; beyond that centrifugal tension reduces the grip available and special belt construction is needed.
This calculator takes 3 inputs: Driver pulley diameter, Driver speed, Driven pulley diameter. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.