Motor speed calculator (poles, Hz, VFD)
Get the RPM of an induction motor and how it changes when a VFD varies the frequency.
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How it is calculated
synchronous rpm = 120 × f / p
actual rpm = synchronous × (1 − slip)
At 60 Hz a 4-pole motor turns at 1800 rpm synchronous and about 1750 rpm actual; at 50 Hz, 1500 and about 1450 rpm.
On a VFD, speed is proportional to frequency. Above rated frequency the motor runs at constant power and loses torque.
Frequently asked questions
What RPM is a 4-pole motor at 60 Hz?
1800 rpm synchronous; with 3 % slip, about 1746 rpm.
Can a VFD run a motor faster than rated speed?
Yes, by raising the frequency, but torque drops above base speed and bearings and cooling must be checked.