Pulley speed calculator
Find the driven pulley speed and the belt speed of a belt drive from the driver speed and the two pulley diameters.
How it is calculated
Driven speed N2 = N1 × D1 ÷ D2. Belt speed v = π × D1 × N1 ÷ 60,000 (D1 in mm, gives m/s).
Worked example
Motor at 1750 rpm, driver 100 mm, driven 250 mm: N2 = 1750 × 100 ÷ 250 = 700 rpm, belt speed = 9.16 m/s.
Steps
- Enter the driver speed from the motor nameplate.
- Enter both pulley diameters.
- Read the driven speed and check the belt speed against the belt rating.
Frequently asked questions
Does belt slip change the speed?
Yes. Real V-belt drives lose about 1 % to 2 % from slip, so the actual driven speed is slightly lower.
Which speed do I use for the belt rating?
Use the belt speed. Most V-belt ratings are checked against m/s, and high speed (above about 30 m/s) needs special belts.
Can I use outside diameter?
Use pitch diameter for accurate ratios. Outside diameter gives a small error.
Related calculators
References
Speed ratio and belt speed relations from standard belt drive design (Shigley, Mechanical Engineering Design).
Estimates for information only. Verify critical values with a qualified engineer or your supplier standards.