Motor Synchronous Speed and Slip Calculator
Synchronous speed of an AC motor from the supply frequency and number of poles, and the slip of an induction motor from its nameplate speed.
Results
Synchronous speed
1500.0
rpm
Slip
3.33
%
Slip in rpm
50.0
rpm
Rotor current frequency
1.667
Hz
What this tool does
The magnetic field in an AC motor turns at 120 × f ÷ p revolutions per minute, so a 4-pole motor on 50 Hz has a 1500 rpm field and on 60 Hz 1800 rpm. An induction motor always runs a little slower — typically 1 to 5 % at full load — because the rotor needs that slip to have current induced in it; a nameplate saying 1450 rpm is a 4-pole motor with 3.3 % slip. With a frequency inverter the same formula tells you the speed at any drive frequency.
Formula
n_s = 120 f ÷ p · s = (n_s − n) ÷ n_s
Variables
| Symbol | Meaning | Unit |
|---|---|---|
f | Supply frequency | Hz |
p | Number of poles | — |
n | Rated speed (nameplate) | rpm |
NS | Synchronous speed | rpm |
S | Slip | % |
SR | Slip in rpm | rpm |
FR | Rotor current frequency | Hz |
Worked example
- Supply frequency50 Hz
- Number of poles4
- Rated speed (nameplate)1450 rpm
- Synchronous speed1500.0 rpm
- Slip3.33 %
- Slip in rpm50.0 rpm
- Rotor current frequency1.667 Hz
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.