Motor Slip Calculator
Calculate induction motor slip and what it reveals about loading.
About Motor Slip Calculator
Slip is roughly proportional to torque, so comparing measured slip with rated slip gives a non-invasive estimate of motor loading. Rotor current frequency is slip times supply frequency, which is why rotor losses are low at normal slip. Slip measurement is the standard field technique for finding oversized motors, which run at poor efficiency and power factor.
Formula
Motor Slip
Slip % = (n_s − n_r) ÷ n_s × 100; load ≈ slip ÷ rated slip
- rotor frequency
- Slip times supply frequency, the frequency of induced rotor currents
Worked example
With the default values below, Motor Slip Calculator returns Slip of 3.000%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Synchronous speedminimum 1 rpm
- 1,500 rpm
- Measured rotor speedminimum 0 rpm
- 1,455 rpm
- Rated slip at full loadaccepts 0.01–20 %
- 3 %
Results
- Slip
- 3.000%
- Slip
- 45.00 rpm
- Estimated Load
- 100.0%
- Rotor Current Frequency
- 1.500 Hz
- Verdict
- Well loaded
Step by step
- 1Values used
- 2Motor Slip
- 3Slip= 3.000
- 4Slip= 45.00 rpm
- 5Estimated Load= 100.0
- 6Rotor Current Frequency= 1.500 Hz
- 7Verdict= Well loaded
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Motor Slip calculated?
Slip % = (n_s − n_r) ÷ n_s × 100; load ≈ slip ÷ rated slip Slip is roughly proportional to torque, so comparing measured slip with rated slip gives a non-invasive estimate of motor loading. Rotor current frequency is slip times supply frequency, which is why rotor losses are low at normal slip.
Why does Motor Slip matter?
Slip measurement is the standard field technique for finding oversized motors, which run at poor efficiency and power factor.
What values do I need to enter?
This calculator takes 3 inputs: Synchronous speed, Measured rotor speed, Rated slip at full load. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.