How it works
Apparent power (kVA) is the voltage times the current, without regard to how much of it does real work. Real power (kW) is apparent power times the power factor. In a balanced three-phase system the line-to-line voltage times the line current is multiplied by √3 (1.732) because the three phases are 120° apart.
Equipment such as transformers and generators is rated in kVA because it carries the current regardless of power factor, while loads are often quoted in kW. This tool converts among the three.
Worked example
100 A on a 480 V three-phase system at a 0.9 power factor:
- kVA = √3 × 480 V × 100 A ÷ 1,000 = 83.14 kVA
- kW = 83.14 × 0.9 = 74.82 kW
- Current = 100 A (given)
| Input | Value |
|---|---|
| I know | Amps |
| System | Three-phase |
| Line voltage | 480 V |
| Power factor | 0.9 |
| Amps (if known) | 100 A |
| kW (if known) | 75 kW |
| kVA (if known) | 83 kVA |
| Result | Value |
|---|---|
| Current | 100 A |
| Apparent power | 83.14 kVA |
| Real power | 74.82 kW |
Assumptions and limits
- Balanced three-phase loads and line-to-line voltage. Unbalanced loads and line-to-neutral loads need per-phase calculation.
- Sinusoidal waveforms. Harmonic-rich loads draw more current than these formulas show.
- Power factor is your input; it varies with load, especially for motors.
Common questions
How do I convert kVA to amps?
For single-phase divide kVA × 1,000 by the voltage; for three-phase divide by √3 times the voltage.
What is the difference between kW and kVA?
kVA is apparent power and kW is real power. They are equal only at a power factor of 1.
Why is √3 in the three-phase formula?
The three line currents are 120° out of phase, so the total apparent power is √3 times the line voltage and line current.
What power factor should I use?
Use the value on the equipment’s data sheet or measure it; resistive loads are near 1.
Sources
- Standard AC power relationships: S = V × I (single-phase), S = √3 × V × I (three-phase balanced), P = S × PF.
Updated 2026-09-30