kW is the amount of ‘actual power’ an electrical system has. This shows you how much power is being converted into useful, working output.
kVA on the other hand is the measure of ‘apparent’ power. If kW is how much power you can work with, kVA tells you how much is being used in the system overall.
If the efficiency of an electrical system is perfect, then kW would be equal to kVA. But because no system is completely efficient, not all of the apparent power will be converted into useful output.
To convert kW to kVA, you first need to know the efficiency (or power factor) of the system. Power factor (pf) is measured on a scale from 0 to 1.
On average, a generator will have a power factor of 0.8.
The formula for converting kW to kVA is: kW / pf = kVA e.g. 200 kW / 0.8 pf = 250 kVA
The formula for converting kVA to kW is: kVA x pf = kW e.g. 250 kVA x 0.8 pf = 200 kW
While it can be helpful to have a good idea of the generator size you need, don’t worry if you’re unsure, or you don’t feel confident converting between kW and kVA yourself.