When you need this conversion
Generator sets, UPS systems, and inverters are often rated in kVA (apparent power) while the appliances they run are rated in kW (real power). Sizing a backup power system correctly means converting between the two, especially for solar-plus-generator hybrid systems where a genset tops up batteries alongside an inverter.
The formula in plain terms
Real power equals apparent power multiplied by the power factor: kW = kVA times PF. Power factor describes how efficiently a load turns supplied power into usable work. A power factor of 1.0 means all the apparent power is usable; a lower power factor, common with motors, pumps, and welders, means some power is reactive and does no work. Most generators and inverters assume a 0.8 power factor unless stated otherwise. To reverse the calculation and go from kW to kVA, divide: kVA = kW divided by PF.
Common kVA to kW values (0.8 power factor)
| kVA | kW (at 0.8 PF) |
|---|---|
| 5 kVA | 4 kW |
| 10 kVA | 8 kW |
| 15 kVA | 12 kW |
| 20 kVA | 16 kW |
| 50 kVA | 40 kW |
Practical tips
Match power factor to the load
If your setup is mostly resistive, lighting, heaters, resistive water pumps, use a power factor closer to 0.9-1.0. If it is dominated by motors, air conditioners, or refrigeration compressors, use 0.7-0.8 to avoid undersizing.
Size for starting current, not just running load
Motors and compressors draw a surge current at startup that can be three to seven times the running load. Even after converting kVA to kW correctly, add headroom for motor starting or check the generator's surge rating separately.
Do not confuse kVA rating with continuous output
A generator's kVA plate rating is a maximum; continuous safe output is usually 80-90 percent of that figure for extended runs.