MOTORS · CALCULATOR

Motor slip calculator

Free motor slip calculator: get slip from synchronous speed and rotor speed. The formula and a worked example are shown; verify against the NEC.

Written by Chameera Sampath · Not yet reviewed by a licensed electrician. See the methodology.

US (NEC) only · NFPA 70 / NEC — locally adopted editionDefaults are US values. Verify the locally adopted NEC edition and project data.Official reference ↗

Project inputs

Measurements

Synchronous speed

rpm

Rotor speed

rpm

Updates as inputs change. Unit changes preserve the same physical values.

THE MATH BEHIND THE ANSWER

Method & assumptions

Slip = (Ns − Nr) / Ns × 100

Negative slip corresponds to generating operation.

Results do not check every aspect of an electrical installation. The calculators follow US (NEC) practice only; a regional preset changes defaults such as voltage and units, and no result certifies NEC compliance.

Sources and validation →

Worked example

Synchronous speed: 1,800 rpm · Rotor speed: 1,750 rpm

Slip: 2.778 %

This example uses the stated inputs; results for the entered values appear above.

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