Three-phase power is the standard method of generating, transmitting, and distributing alternating current (AC) electricity in industrial and commercial facilities. Instead of a single alternating waveform, a three-phase supply delivers three currents offset by 120 degrees.
The portion of electricity that performs actual work — turning a motor shaft, heating an element, or lighting a space.
The total power the supply and generator must deliver. It is the vector sum of real power and reactive power.
Power that inductive loads (motors, transformers) store and return each cycle without performing useful work.
Line-to-line voltage is measured between any two of the three phase conductors and is the value used in three-phase power formulas. Line-to-neutral voltage is measured between one phase conductor and neutral and equals the line-to-line value divided by √3. For this calculator, enter the line-to-line voltage.
The actual work performed. Measured by your utility meter. This is the number the calculator produces.
Total power the generator must supply. Generator alternators are rated in kVA because their limit is current and voltage.
Power stored and returned by inductive loads. Raises kVA demand without raising kW output.
PF = kW ÷ kVA. A purely resistive heater has PF = 1.0. An inductive motor may sit at 0.7–0.9. The generator must supply more kVA than the kW rating suggests.
Enter your line-to-line voltage, current, and power factor to calculate real power (kW), apparent power (kVA), and reactive power (kVAR). Switch to single-phase mode or calculate amps from kW with a single click.
Results are estimates for planning. Confirm final sizing with an engineer.
For a quick reference at the standard generator power factor of 0.8, the table below lists the full-load current for common generator kilowatt ratings at 400 V (IEC/global standard) and 480 V (North American industrial).
| Generator kW | Amps @ 400 V | Amps @ 480 V |
|---|---|---|
| 5 kW | 9.0 A | 7.5 A |
| 10 kW | 18.0 A | 15.0 A |
| 20 kW | 36.1 A | 30.1 A |
| 50 kW | 90.2 A | 75.2 A |
| 100 kW | 180.4 A | 150.4 A |
| 200 kW | 360.8 A | 300.7 A |
| 500 kW | 902.1 A | 751.8 A |
Seeing the formula in action makes it easier to trust the result. Here are three common scenarios that show how the calculator arrives at its numbers.
A three-phase motor draws 10 A at 415 V with a power factor of 0.9. kW = (1.732 × 415 × 10 × 0.9) ÷ 1000 = 6.47 kW.
A production line draws 30 A at 480 V with a power factor of 0.85. kW = (1.732 × 480 × 30 × 0.85) ÷ 1000 = 21.2 kW.
A 100 kW three-phase generator at 400 V and 0.8 power factor. Amps = (100 × 1000) ÷ (1.732 × 400 × 0.8) = 180.4 A.
A kilowatt figure alone does not tell you which generator set to buy. Convert kW to kVA by dividing by the power factor: at 0.8 PF, a 100 kW load requires a 125 kVA generator. Add a 25% margin for starting surge and match to a standard rating.
Final generator selection should be checked against the complete load schedule, motor-starting sequence, power factor, site conditions, duty rating and selected engine-alternator combination before equipment is ordered.
At Shandong Huali Electromechanical Co., Ltd., we manufacture diesel generator sets engineered for continuous industrial operation, with over 25 years of experience and strict pre-delivery testing on every unit. If your calculation points to a load we can serve, our engineers will confirm the correct rating for your application.
A: Multiply line-to-line voltage by line current by power factor by 1.732, then divide by 1000: kW = (√3 × V × I × PF) ÷ 1000.
A: At 400 V and 0.8 power factor, 100 kW draws approximately 180 amps. At 480 V, the same 100 kW draws about 150 amps. Higher voltage means lower current.
A: kW is real power that performs useful work; kVA is apparent power that the generator must supply. They are related by power factor: kW = kVA × PF.
A: Use 1.0 for resistive loads (heaters), 0.8 for a typical mixed industrial or generator load, and 0.7–0.9 for motors and compressors. When in doubt, 0.8 is the accepted generator convention.
A: Yes. Switch the calculator to single-phase mode and the tool drops the √3 constant automatically, using kW = (V × I × PF) ÷ 1000.
A: Convert kW to kVA by dividing by the power factor, add a 25% margin for starting surge, and round up to the nearest standard generator rating.
