Motor Full-Load Current Calculator
kW → AMPS · 1φ / 3φHow it is calculated
Three-phase: I = P / (√3 × U × cos φ × η)Single-phase: I = P / (U × cos φ × η)
P in watts, U line-to-line voltage, η efficiency as a fraction. Typical induction motors: cos φ ≈ 0.85, η ≈ 0.90–0.95. Always verify against the motor nameplate — this calculator is for pre-selection, not for replacing nameplate data.
FAQ
Why is my measured current lower than calculated?
The formula gives full-load current. A motor at partial load draws less — and at very light load the power factor also drops, so current does not fall linearly with load.
Which value do I use for cable and breaker sizing?
Size cables and protection from the nameplate full-load current (In), applying your local code (e.g. IEC 60364) derating factors — not from a calculator estimate.
Does a VFD change the input current?
Yes. A drive draws non-sinusoidal current and its input current can differ from motor current; size drive input cabling per the drive manual, not the motor formula.