The Nameplate Is a Ceiling, Not a Promise
A generator's kVA rating says: I can push this much current without overheating, at any power factor. The kW it actually delivers is decided by the load — how much of that current comes back as work instead of sloshing between source and load. Motors, transformers, and fluorescent lighting all have coils and iron that shift the current waveform out of phase with the voltage. The cosine of that phase shift is the power factor, and it is the single number that converts the machine's rating into the site's real power draw.
kW = kVA × power factor
P = S · cos φ
PF is a number between 0 and 1 — 1.0 for pure resistance, ~0.8 for a motor-heavy site.
Common Ratings at Real Power Factors
| kVA | PF | kW | Context |
|---|---|---|---|
| 5 kVA | 0.8 | 4 kW | Small RV/backup generator — the nameplate 5,000 VA at mixed loads. |
| 10 kVA | 0.8 | 8 kW | Construction-site generator running tools and pumps. |
| 10 kVA | 1.0 | 10 kW | Same machine feeding only resistive heaters. |
| 50 kVA | 0.8 | 40 kW | Commercial transformer feeding a small building. |
| 100 kVA | 0.9 | 90 kW | PFC-corrected office load — better PF, more kW per kVA. |
The 10 kVA row pair is the lesson: the identical machine swings from 8 kW to 10 kW depending on what is plugged in. That is why two sites with the same generator can pay wildly different electricity bills, and why a PF correction capacitor bank — which lifts a site's PF from 0.7 toward 0.95 — can free up 20% of a transformer's real capacity without buying new iron. The kVA ceiling never moves; the kW that fits under it does.
Engineering Context
Running the conversion backwards — finding the kVA you must buy for a known kW load — is the kW to kVA page, the UPS-sizing calculation. If you only need the raw power numbers without the phase-angle picture, the straight unit work lives in watts to kW and kW to watts on the energy hub. The motors that drag a site's PF down are rated in horsepower to kW, and the current those same kW pull at 120/240 V is the watts to amps question. All of it returns to the electric hub.
More: kW to kVA · Power Factor · W to kW · Electric Hub
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Frequently Asked Questions
How do I convert kVA to kW?
Multiply by the power factor: kW = kVA × PF. A 10 kVA generator feeding a load at 0.8 PF delivers 10 × 0.8 = 8 kW of real power. The PF is the cosine of the phase angle between voltage and current — use 0.8 when the load mix is unknown.
Why are generators and transformers rated in kVA instead of kW?
Because the machine's limiting factor is current — heat in the windings — and current is set by apparent power (kVA), regardless of the load's power factor. A generator rated 10 kVA can safely deliver 10 kVA of current at any PF; the kW it produces depends on what the load actually converts to work. The 0.8 figure on many nameplates is the PF the machine is guaranteed to support, not what every load will present.
What power factor should I use for typical loads?
Resistive loads — heaters, incandescent lamps — sit at 1.0. Induction motors run 0.7 to 0.85, worse when lightly loaded. Modern switched-mode power supplies with PFC correction reach 0.95 to 0.99. If you are sizing a generator for a mixed site and have no measurements, 0.8 is the conservative industry default.