When sizing a generator, understanding the difference between kVA and kW is essential.
What is kW?
kW (kilowatts) is the amount of real power being used to do actual work — for example, running lighting, heating, or equipment.
It’s the power you’re actually paying for and what your machinery truly consumes.
What is kVA?
kVA (kilovolt-amperes) is the apparent power — the total power supplied by the generator.
It includes both:
Real power (kW)
Reactive power (the extra energy needed to create magnetic fields in motors, transformers, etc.)
Generators are typically rated in kVA, because they must supply both real and reactive power.
The Key Difference: Power Factor
The relationship between kVA and kW depends on something called power factor (PF).
Formula:
kW = kVA × Power Factor
Most generators are rated at a 0.8 power factor.
So for example:
100 kVA × 0.8 = 80 kW
200 kVA × 0.8 = 160 kW
This means a 100 kVA generator will usually deliver 80 kW of usable power.
Why It Matters When Choosing a Generator
If you size a generator based only on kW without considering kVA (and power factor), you could overload the machine.
Resistive loads (heaters, filament lighting) are close to 1.0 PF
Inductive loads (motors, compressors, pumps) usually have a lower PF and require more kVA
That’s why generators are specified in kVA — it ensures they can handle the total electrical demand.
Simple Rule of Thumb
If you're unsure:
Multiply kVA by 0.8 to estimate kW output.
Understanding this difference helps you choose a generator that runs efficiently, avoids overloads, and keeps your site powered without issues.