EleCanada
Motor speed relationships

Induction motor speed calculator

Calculate synchronous speed, rotor speed, slip, or speed regulation from supplied motor data.

Calculation inputs

Motor speed inputs

Slip from a measured rotor speed
Hz

Enter the frequency applied to the motor. No 60 Hz value is assumed.

poles
rpm

For induction-motoring operation, this must be below synchronous speed.

Enable JavaScript to calculate. The method and scope remain below.

Motor speed result

Enter the motor data for the selected calculation.

This is a physical speed relationship using the supplied inputs. It is not a motor performance test, load diagnosis, equipment selection or code determination.

Inputs and interpretation

Use the supply frequency and total number of motor poles to calculate synchronous speed. For the slip mode, enter either a measured rotor speed or a supplied percent slip. The speed-regulation mode compares the same motor's no-load and full-load speeds.

Inputs are required; frequency is not pre-filled. The calculator does not infer a motor pole count, expected slip, load, or normal operating range from a nameplate.

Formula and examples

The source defines synchronous speed as ns = 60 × f ÷ p, where f is supply frequency in hertz and p is the number of pole pairs. This interface asks for total poles P and uses the equivalent ns = 120 × f ÷ P.

Slip speed is ns − nr; percent slip is 100 × (ns − nr) ÷ ns. Rotor speed from slip is nr = ns × (1 − s), where s is slip as a fraction.

Speed regulation is 100 × (no-load speed − full-load speed) ÷ full-load speed. The guide's examples include 60 Hz with two poles and 5% slip, giving 3,420 rpm, and 1,790 rpm no-load versus 1,740 rpm full-load, giving 50 rpm and about 2.87% regulation.

Limits and interpretation

The slip model is limited to the positive motoring range of a three-phase induction motor: rotor speed from standstill up to, but below, synchronous speed, or slip above 0% through 100%. It does not model generating or regenerative operation, a synchronous motor, a drive's commanded frequency, acceleration, torque or load-dependent performance.

Calculated rotor speed from a supplied slip is a mathematical result, not a measured or guaranteed operating speed. Speed regulation only compares the two speeds supplied; it does not grade the motor or establish an acceptable range.

No motor selection, electrical code, protection, efficiency or installation decision is provided.

Common questions

Does the calculator assume Canada's 60 Hz supply?

No. Enter the frequency supplied to the motor. The page does not insert a frequency default.

Why is measured rotor speed below synchronous speed?

In induction-motoring operation, rotor speed differs from the rotating stator field; that difference is slip. This calculator does not assess whether the measured slip is normal for the motor or load.

Does speed regulation describe the full motor curve?

No. It compares only the no-load and full-load speeds you enter using the source's definition.

Motor currentConvert mechanical shaft power or estimate motor current from matching full-load data.Electrical relationshipsSolve DC quantities, convert AC power/current, compare PF current ratios, or relate balanced wye voltages.Voltage dropEstimate voltage loss or maximum distance from supplied impedance.

Source

British Columbia Industry Training Authority, Construction Electrician Apprenticeship Program, Level 3, Learning Guide H-5: Install AC Motors and Alternators, Version 1, corrected January 2017, Learning Task 2, printed pages 28–31. The guide supplies the synchronous speed, slip and speed-regulation definitions and examples. It is Canadian trade-training material, not a provincial code or motor-selection approval.

Source and terminology checked November 10, 2026. Report a problem or suggest a source; inputs are not attached automatically.