Example
7.5 kW motor on 400 V three phase
The 7.5 kW figure is mechanical output, with 90% motor efficiency and 0.85 power factor.
Electrical input = 7.5 ÷ 0.90 = 8.333 kW Current = 8,333 ÷ (1.732 × 400 × 0.85) = 14.15 A
Result: 14.15 A.
Power calculator
Three-Phase Current Calculator
Calculate balanced three-phase line current while stating whether your power figure is electrical input kW, motor mechanical output kW or apparent kVA.
Estimated line current14.15 A
Calculation breakdown
| Input basis | Motor mechanical output kW |
|---|---|
| Electrical real power | 8.333 kW |
| Apparent power | 9.804 kVA |
| Line-to-neutral voltageDerived for a balanced wye-equivalent relationship | 230.9 V |
I = output kW × 1,000 ÷ efficiency ÷ (√3 × VLL × PF) = 7.5 × 1,000 ÷ 0.9 ÷ (1.732 × 400 × 0.85) = 14.15 A
- This is a balanced steady-state line current. Motor starting current can be several times higher and must come from motor/controller data or measurement.
Before you rely on this
Steady-state current is not sufficient for motor protection, cable or breaker selection. Verify starting behavior, duty, harmonics, derating and applicable installation rules.
Method
How the number is reached
Balanced three-phase apparent power is √3 × line-to-line voltage × line current. Real electrical power is apparent power multiplied by power factor.
A motor nameplate output in kW is mechanical shaft power, so electrical input is higher by the inverse of efficiency. Efficiency is not applied when the entered kW is already electrical input.
Electrical input kW: I = kW × 1,000 ÷ (√3 × VLL × PF) Motor output kW: I = kW × 1,000 ÷ efficiency ÷ (√3 × VLL × PF) Apparent kVA: I = kVA × 1,000 ÷ (√3 × VLL)
Symbols
- VLL
- Line-to-line voltage
- IL
- Current in each line
Worked examples
The same maths, applied
Limits of the model
What it assumes, and where it stops
Assumptions
The supply and load are balanced and values represent steady state.
Not covered
Does not calculate starting current, protective-device settings, conductor size, unbalance or harmonics.
Sources
Where these figures come from
- Electrical Installation Guide (IEC-based)Schneider ElectricReference for single-phase and three-phase power relationships and power factor.
- IEC 60050 — International Electrotechnical Vocabulary (Electropedia)International Electrotechnical CommissionStandard terminology for electrical quantities, including apparent power and power factor.
- SI UnitsNIST Office of Weights and MeasuresDefinitions of the volt, ampere, watt and joule used for the unit conventions on this site.
Next steps
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Watts to Amps Calculator
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Last meaningful update: 2026-08-19. This date changes only when the model, the sources or the guidance change.