Motor Current Calculator
Estimate running current for an AC motor from mechanical horsepower and assumed electrical efficiency and power factor. This can help with preliminary load studies and sanity checks before using nameplate or code-table values.
Physics-based estimate only. Use motor nameplate data and applicable code tables when those values govern conductor, overload or protective-device sizing.
How this tool works
Three-phase current ≈ HP × 746 ÷ (√3 × V × efficiency × power factor). Single-phase current omits the √3 factor.
Example
A 50 hp, 480 V three-phase motor at 92% efficiency and 0.88 power factor draws an estimated current near the mid-50 amp range.
Common questions
Is this the NEC full-load current?
No. Code tables and nameplate current can differ from a physics-based estimate and should be used where required.
Does this include starting current?
No. Locked-rotor and starting current are separate from normal running current.