Two power ratings that look similar but aren't identical — the gap between them is where a sizing mistake can hide.
kW is real power; kVA is apparent power
kW (kilowatts) measures real power — the power actually doing useful work. kVA (kilovolt-amps) measures apparent power — the total power flowing in the circuit, including power that isn't converted to useful work due to phase differences between voltage and current in AC systems with inductive loads (motors, in particular).
Power factor is the bridge between them
Power factor (a number between 0 and 1) accounts for that phase difference — a power factor of 1.0 means kW and kVA are equal (a purely resistive load); a lower power factor means the kVA rating is higher than the actual usable kW. Motor-heavy loads typically have a lower power factor than simple resistive loads like heaters.
Why generators are sometimes rated in kVA
A generator's kVA rating reflects its total capacity to handle apparent power, which matters because motor-starting loads draw more apparent power than their steady-state kW rating alone suggests — see our surge watts calculator for the related concept of why motor loads need extra headroom.
What this means for sizing
If a spec sheet gives kVA and you need kW (or the reverse), you need the power factor to convert accurately — assuming they're interchangeable can lead to undersizing equipment for real-world loads, particularly ones with lower power factor like certain motors and electronics.
Frequently asked questions
Is kVA always higher than kW?
Yes, for any real-world AC circuit — kVA equals kW only at a perfect power factor of 1.0, which resistive loads approach but inductive loads (motors) typically don't, so kVA is generally equal to or greater than kW.
Do I need to worry about kVA vs kW for a simple home solar inverter?
Less so for typical solar inverters serving resistive and mixed household loads, but it becomes more relevant when sizing a generator for motor-heavy loads like well pumps or AC compressors, where power factor genuinely affects real capacity needed.