Free engineering tool
Motor RPM Calculator
Calculate synchronous speed and actual motor RPM from frequency, pole count, and slip.
Calculator
Calculate motor speed
For induction motors: determine synchronous speed, rotor speed, and slip from the electrical motor data.
Mains or drive output frequency. The value must be greater than 0 Hz.
Total number of magnetic poles, not pole pairs. Use a positive even integer.
Positive while motoring, 0% at synchronous speed, negative while generating, and 100% at standstill.
nₛ = 120 × f / P; n = nₛ × (1 − s)
P is the total pole count; slip s is used as a decimal in the formula.
Rotor speed n: 1,470 rpm
Results
Synchronous speed nₛ
1,500 rpm
Rotor speed n
1,470 rpm
Slip s
2 %
Slip frequency
1 Hz
Angular speed
153.94 rad/s
Operating state
Motoring
The actual speed is a theoretical induction-motor calculation. Load, control, and motor characteristics can affect the measured value.
Formula and calculation method
Synchronous speed follows from supply or drive frequency and pole count. In motoring operation, an induction motor's rotor runs below that speed because of slip.
Synchronous speed: nₛ = 120 × f / P (P = total pole count)
Rotor speed: n = nₛ × (1 − s)
Slip: s = (nₛ − n) / nₛ · Rotor frequency: f₂ = s × f
Assumptions and limitations
- Pole count means the total number of poles and must be even; pole pairs p = P/2.
- Negative slip indicates generating operation, 0% synchronous operation, and 100% standstill.
- The loaded-speed relation applies to induction machines. Synchronous and permanent-magnet motors follow synchronous speed in steady state.
- Drive command frequency, slip compensation, and actual shaft speed can differ.
Technical sources
Formulas and conventions were checked against these primary and manufacturer references.