Free Engineering Tool
Power and motors
Motor Speed and Slip Calculator
Choose the pole count and supply frequency for the synchronous speed. Add the measured rpm to get slip and rotor frequency.
- Free
- No sign-up
- Runs in your browser
- Your numbers never leave your device
Inputs
Supply frequency
Hz
rpm
Use a non-contact tachometer on the shaft for the real speed under load.
Readout
Ns-rpm synchronous
0rotor speed vs synchronousNs
SLIP-%
Slip speed
-rpm
Rotor frequency
-Hz
Formulas
Ns = 120 × f / P · slip s = (Ns − N) / Ns · frotor = s × f
Synchronous speeds
| Poles | 50 Hz | 60 Hz |
|---|---|---|
| 2 | 3000 | 3600 |
| 4 | 1500 | 1800 |
| 6 | 1000 | 1200 |
| 8 | 750 | 900 |
| 10 | 600 | 720 |
| 12 | 500 | 600 |
Reading the slip
- A healthy loaded induction motor typically runs at roughly 1% to 5% slip, with small machines at the higher end.
- Slip well above the nameplate value at the same load suggests low supply voltage, an overload, or a rotor problem.
- Slip near zero means little load. A speed above synchronous means the machine is being driven as a generator.
Frequency checks matter too: see how to measure frequency.
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