Electric Motors
Motor Slip Calculator
Calculate motor slip from synchronous speed and measured speed. The default values illustrate the workflow; replace them with measurements or ratings from one documented condition.
Enter values for Motor slip
Enter ratings or measurements that describe one scenario.
Motor slip: calculation method
This page evaluates slip = (Ns − N) ÷ Ns × 100. The entered quantities are Synchronous speed and Measured speed.
With the current entries, the primary answer is 4.00%. Preserve the raw inputs when replacing this example.
Calculate motor slip from synchronous speed and measured speed. The nearest even pole count step is handled by Motor Poles Frequency Calculator.
Preparing the calculation
Separate shaft output power from electrical input power. Nameplate and meter values are not interchangeable unless they describe the same condition.
A denominator entry cannot be zero. Use the displayed unit for every field and document conversions separately. If you also need round-trip efficiency, continue with Battery Round-Trip Efficiency Calculator.
- Synchronous speed
- Default example: 1500 rpm. Enter synchronous speed in rpm.
- Measured speed
- Default example: 1440 rpm. Enter measured speed in rpm.
Interpreting the answer
Use Motor slip as one quantified check within the larger decision. Compare it with starting demand, running current, torque, efficiency, slip, and thermal loading.
A result without its source conditions is difficult to compare or audit. For the companion synchronous speed calculation, open Synchronous Motor Speed Calculator.
A second scenario
Change Synchronous speed from 1500 rpm to 1800 rpm and leave all other entries untouched. The displayed value changes from 4.00% to 20.00%.
Keep both cases when the changed input represents genuine uncertainty.
Checks before using the answer
Use stable loaded speed.
The surrounding system may introduce voltage imbalance, drive waveform, transient torque, and bearing load. Use measurements, manufacturer data, or another calculation for effects that can change the decision.
Use nameplate data and measurements from the same load and supply condition.
Common questions before using the result
How should I compare two Motor Slip cases?
Change one uncertain entry at a time and preserve the baseline. Use nameplate data and measurements from the same load and supply condition.
Does the answer include a design margin?
The calculator does not approve equipment or supply an unexplained margin. Compare against starting demand, running current, torque, efficiency, slip, and thermal loading.
Why does Motor slip show several decimals?
Do not round between dependent calculations. Match the final display to the precision of the source data.
Which input can create an undefined result?
Synchronous speed is used in a denominator and must be greater than zero.
How should I prepare the Motor Slip inputs?
Choose entries that describe the same case. Separate shaft output power from electrical input power.