The short answer
kW measures real power, which is the power that performs useful work such as turning a motor shaft, heating an element, or running electronic equipment.
kVA measures apparent power, which combines real power and reactive power. It describes how much total electrical capacity the supply equipment must provide.
The conversion
For AC systems, the basic relationship is kW = kVA x power factor. If a 100 kVA generator supplies a load at 0.8 power factor, the real power available is 80 kW.
At unity power factor, kVA and kW have the same numerical value. Below unity, the kW value is lower than the kVA value.
- 100 kVA at 1.0 PF = 100 kW
- 100 kVA at 0.9 PF = 90 kW
- 100 kVA at 0.8 PF = 80 kW
Why equipment uses kVA ratings
Transformers, generators, and UPS systems are often rated in kVA because heating and capacity limits are driven by voltage and current. Those limits exist whether the connected load has a high or low power factor.
Load planning should therefore consider both values: kVA for source and conductor capacity, and kW for the useful work the load actually needs.