MOTORS · CALCULATOR

Motor current, voltage and power calculator

Free motor current, voltage and power calculator: get motor current from shaft output, voltage, current, power factor and efficiency. With the formula shown.

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

Solve forShaft output

Voltage

Power factor

Efficiency

Supply

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

THE MATH BEHIND THE ANSWER

Method & assumptions

I = P / (k × V × PF × η); V = P / (k × I × PF × η); P = k × V × I × PF × η; k = 1 or √3, P in W = hp × 745.7

Balanced steady operation at one operating point; efficiency and power factor vary with load. The NEC table full-load current, the nameplate current and the starting current all differ from this arithmetic, and a motor supply voltage is never chosen from arithmetic alone.

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

Solve for: Current · Shaft output: 5 hp · Voltage: 230 V · Power factor: 0.85 · Efficiency: 90 % · Supply: Single phase

Motor current: 21.191 A

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

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