Motor Speed Calculator

AC electric motors spin at a speed determined by the frequency of their power supply and the number of magnetic poles built into them — the Motor Speed Calculator works out that speed for you. Enter your Supply Frequency (typically 50 Hz or 60 Hz) and Number of Poles to get the Synchronous Speed in RPM. Secondary outputs include speed in RPS and the estimated Actual Speed at 5% slip, which reflects the slightly reduced speed of real induction motors under load.

Hz

Power supply frequency (typically 50Hz or 60Hz)

Total number of magnetic poles (must be even)

Results

Synchronous Speed

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Speed in RPS

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Actual Speed (5% slip)

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Frequently Asked Questions

How do you calculate motor speed from frequency and poles?

Motor synchronous speed is calculated using the formula: RPM = (120 × Frequency) / Number of Poles. The constant 120 comes from 60 seconds per minute times 2 for the AC cycle.

What is the difference between synchronous speed and actual motor speed?

Synchronous speed is the theoretical speed of the rotating magnetic field. Actual induction motor speed is slightly lower due to slip, typically 2-5% less than synchronous speed.

Why must the number of poles be even?

Motor poles must be even because they come in pairs (north and south). Common pole counts are 2, 4, 6, 8, etc. More poles result in lower speed but higher torque.

What are standard power frequencies used worldwide?

Most countries use either 50Hz (Europe, Asia, Africa) or 60Hz (North America, parts of South America). Some applications may use higher frequencies for specialized motors.

How does frequency affect motor speed?

Motor speed is directly proportional to frequency. Higher frequency increases speed, while lower frequency decreases speed. This principle is used in variable frequency drives (VFDs).

What is slip in an induction motor?

Slip is the difference between synchronous speed and actual rotor speed, expressed as a percentage. Typical slip ranges from 2-5% at full load for standard induction motors.