kW to kVA calculator
Convert kilowatts (real power) to kilovolt-amperes (apparent power), or the other way round, using the power factor cos φ. You also see the reactive power.
In kW or in kVA, depending on your choice.
Between 0 and 1. For generators and UPS systems 0.8 is common.
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How it's worked out
How it works
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Instant answer
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See the working
Under "How it's worked out" you see the steps, handy for checking your own calculation.
The difference between kW and kVA
- kW is real power: what an appliance actually turns into heat, light or movement.
- kVA is apparent power: voltage × current, which is what the supply and a generator have to provide.
- They are linked by the power factor: kW = kVA × cos φ.
A 100 kVA generator with a power factor of 0.8 can therefore deliver 80 kW of real power. The other way round, an 80 kW load at 0.8 needs a generator of at least 80 ÷ 0.8 = 100 kVA.
Reactive power
The difference between the two is the reactive power in kvar: √(kVA² − kW²). It swings back and forth between source and load without doing useful work, but it still loads cables and the generator. For 80 kW at 0.8 it is 60 kvar.
Which power factor?
For generators and UPS systems 0.8 is common; modern UPS units are often rated at 0.9 or 1. Electric motors are usually between 0.8 and 0.9, and heaters and incandescent bulbs are at 1. Check the rating plate for the exact figure.
To go from power to current, use watts to amps.
Worked examples
| Given | cos φ | Result |
|---|---|---|
| 80 kW | 0.8 | 100 kVA and 60 kvar |
| 50 kVA | 0.9 | 45 kW |
| 10 kVA UPS | 0.9 | 9 kW |
| 30 kW | 1 | 30 kVA |
Sizing a generator
Add up the real power of everything that will run at the same time, divide by the power factor, and leave a margin for starting currents, since motors draw several times their rated current for a moment. A load of 80 kW at 0.8 needs at least a 100 kVA generator, and a 125 kVA one is a more comfortable choice.
Correcting the power factor
Large industrial users add capacitors to bring the power factor closer to 1, which lowers the current, the cable losses and often the network charges. The calculator's kvar line shows how much reactive power such a correction has to supply. To translate kW into the current per phase, use watts to amps.
Frequently asked questions
Why are generators rated in kVA and not kW?
Because the generator has to supply the current, and the current depends on the apparent power. A load with a poor power factor draws more current for the same kW, so the kVA figure is the true limit.
Can kVA be lower than kW?
No. The power factor is at most 1, so real power in kW is never larger than apparent power in kVA. They are equal only for purely resistive loads.
Which power factor do I use if I do not know it?
0.8 is the usual assumption for generators and mixed loads, and it is the safe choice. If you know the load is heating or lighting, use 1.
How do I convert kVA to amps?
For three-phase, I = kVA × 1000 ÷ (√3 × 400 V). 100 kVA at 400 V is about 144 A. For single-phase, divide by the voltage.