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Motor Current Calculator: kW / HP to Amps
Convert motor kW or HP to running current. Results include the values and assumptions used.
Formula and worked example
I = Pinput × 1000 / (k × V × PF)
Pinput = Pshaft / η; k = 1 (single phase), √3 (three-phase L-L), or 3 (three-phase L-N).
Pinput = Pshaft / η; k = 1 (single phase), √3 (three-phase L-L), or 3 (three-phase L-N).
How to use the calculation
For shaft-output kW, enter efficiency as a percentage; the calculation converts it to a fraction before dividing. If the entered kW is already electrical input, efficiency is not applied again. Mechanical horsepower is converted using 1 HP = 745.6999 W.
Worked example
For 7.5 kW shaft output, 90% efficiency, PF 0.85 and 415 V L-L three-phase supply, electrical input is 8.3333 kW and estimated line current is about 13.64 A.
Common questions
Is running current the same as motor starting current?
No. This tool estimates steady running current. Starting method, motor characteristics and operating load are separate considerations.
Which power factor and efficiency should I use?
Use the motor nameplate, manufacturer data or suitable measurements. The worked example is a calculation demonstration, not a universal motor rating.
Can this result choose a cable or breaker?
It supplies one input to further design. Cable installation conditions, starting current and protection characteristics still need separate checks.
Related electrical guides
More electrical calculators
kVA ↔ AmpsConvert kVA to amps, or amps back to kVA.Electricity CostEstimate energy units and cost for multiple loads.Voltage DropCheck voltage drop using copper or datasheet R/X.Power Factor / kVAREstimate kvar needed to improve lagging power factor.Ohm’s LawFind V, A, Ω and W from two known values.
Formula references
Formula review: 31 October 2026. Examples are illustrative; use your actual equipment and project data.
