kVA, kW and Amps Calculator (Single and Three Phase)
Enter one of current, real power or apparent power, with the voltage and power factor. See the other two, and the reactive power, for a single-phase or a balanced three-phase load.
- Current
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- Real power
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- Apparent power
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- Reactive power
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Assumptions
- Voltages and currents are RMS values of a sine-wave supply.
- Three phase: a balanced load, with the line-to-line voltage and the line current.
- Power factor is the ratio of real power (kW) to apparent power (kVA).
Checked 28 October 2026 Kuphaldt, Lessons in Electric Circuits Vol. II (LibreTexts) 11.2: true, reactive and apparent power All sources
How it is calculated
- Single phase: S = V × I; P = S × power factor
- Three phase: S = √3 × V(line to line) × I(line); P = S × power factor
- Current from power: I = S ÷ V (single) or S ÷ (√3 × V) (three phase), with S = P ÷ power factor
- Reactive power: Q = S × √(1 − power factor²)
Worked example
A 10 kW single-phase load at 230 V and power factor 0.8.
| You enter | |
|---|---|
| Supply | Single phase |
| What you know | Real power (kW) |
| Value | 10 |
| Voltage | 230 V |
| Power factor | 0.8 |
| You get | |
| Current | 54.35 A |
| Real power | 10 kW |
| Apparent power | 12.5 kVA |
| Reactive power | 7.5 kVAR |
At 230 V and power factor 0.8, 10 kW of real power means 12.5 kVA and 54.35 A.
Questions
What is the difference between kW and kVA?
kW is the real power that does work (heat, motion). kVA is the apparent power the supply has to carry, including the part that only flows back and forth. kW = kVA × power factor.
Which voltage do I enter for three phase?
The line-to-line voltage, the one between any two phase wires, such as 400 V or 415 V. In a star (Y) system it is √3 times the phase-to-neutral voltage.
Sources and checks
- Kuphaldt, Lessons in Electric Circuits Vol. II (LibreTexts) 11.2: true, reactive and apparent power
- Kuphaldt (LibreTexts) 11.3: calculating power factor (ratio of true to apparent power; its 0.705 example is a test here)
- Fiore, AC Electrical Circuit Analysis (LibreTexts) 9.3: three-phase connections (line voltage = √3 × phase voltage; its examples 9.3 and 9.5 are tests here)
Last checked: 28 October 2026. This tool passes 7 automatic tests before every release. How we check our tools
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