kVA to kW Calculator
Convert kVA to kW by multiplying by the power factor. Live calculator with generator and UPS sizing examples.
Common conversions
| Input | Result |
|---|---|
| 5 kVA @ PF 0.8 | 4 kW |
| 10 kVA @ PF 0.8 | 8 kW |
| 20 kVA @ PF 0.85 | 17 kW |
| 45 kVA @ PF 0.85 | 38.25 kW |
| 50 kVA @ PF 0.9 | 45 kW |
| 75 kVA @ PF 0.9 | 67.5 kW |
| 100 kVA @ PF 0.95 | 95 kW |
| 100 kVA @ PF 1.0 | 100 kW |
The math behind it
- kW = kVA × PF
- kW = 45 × 0.85
- kW = 38.25
Everything you need to know
Converting kVA to kW tells you how much real, usable power a generator, transformer, or UPS can actually deliver, rather than the total electrical capacity printed on its nameplate. The two figures are rarely the same number, and the gap between them is the single most common source of oversized quotes and undersized installs.
How the kVA to kW formula works
Apparent power (kVA) is the total electrical demand a circuit places on its source: voltage multiplied by current, without regard for how much of that current is doing useful work. Real power (kW) is the fraction that actually turns into heat, light, torque, or whatever the load is built to produce. The power factor is the ratio between the two, so multiplying kVA by PF strips out the reactive component and leaves the real power behind. A purely resistive load, like a space heater or an incandescent bulb, carries a PF of 1.0, so its kVA and kW ratings match exactly. A motor or a switch-mode power supply pulls extra current to build magnetic fields or charge internal capacitors, and that current shows up in the kVA figure without doing any work, which is why its kW rating always sits below its kVA rating.
Why generators and transformers are rated in kVA, not kW
A generator or transformer is built to handle a maximum current and voltage combination before its windings overheat, and that thermal limit is set by amps, not by how much of the current is doing useful work. That's why the nameplate is stamped in kVA. The manufacturer has no way of knowing what power factor your specific load will present, so it publishes the apparent-power limit and leaves it to the buyer to apply the actual load's PF and find the usable real-power output. A 100 kVA generator serving a PF 0.8 load only produces 80 kW of usable output even though the machine is running at its full 100 kVA thermal limit. Reading the kVA number off a spec sheet and assuming it equals available kW is the most common reason people misjudge generator or transformer capacity.
Worked scenario: sizing a job-site generator
A contractor rents a 45 kVA diesel generator to run task lighting, a welder, and a couple of induction motors on a job site, and the combined load runs at PF 0.85. Multiplying 45 kVA by 0.85 gives 38.25 kW of usable real power, about 15% less than the number printed on the rental spec sheet. If the contractor instead assumed the full 45 kVA converted straight to 45 kW, the crew would plan for nearly 7 kW more capacity than the generator can deliver, and the unit would trip on overload well before they expected it to. Running the kVA to kW math before signing the rental agreement tells the crew exactly how many kW of tools and lighting they can safely plug in.
Common applications
Diesel and natural-gas gensets are sold in kVA but consume fuel proportional to kW output. Convert before ordering fuel or sizing the day tank.
UPS labels show VA. Convert to real watts using the rated PF so runtime curves on the datasheet match your actual IT load.
A 100 kVA transformer at PF 0.9 delivers 90 kW of real power. Plan loads against kW, not kVA, to avoid voltage drop and overheating.
Rack power budgets are set in kW, but incoming utility and UPS capacity is specified in kVA. Converting at the facility's design PF, often 0.9-0.95 for modern server supplies, keeps density plans inside the real electrical limit.
Common mistakes
Only resistive loads (PF = 1) make them equal. For most equipment kW is 70-90% of kVA, and ignoring the difference oversizes generators by 20-30%.
Genset ratings reference the machine's design PF, typically 0.8. If your real load PF is lower, you can hit the kVA limit before the kW limit.
Converting kVA to kW is a multiplication, kW = kVA × PF, the reverse of the kW to kVA formula. Dividing by PF instead inflates the real-power estimate instead of shrinking it.
A building's PF often dips during motor startup or HVAC cycling. Sizing off the nameplate PF alone can overstate available kW during the hours when it matters most.
Frequently asked questions
How many kW is a 20 kVA generator?+
16 kW at the common 0.8 power factor rating. Multiply the 20 kVA nameplate figure by the generator's rated PF, 20 × 0.8 = 16, to find the usable real-power output.
How many kW is a 100 kVA generator?+
80 kW at PF 0.8, or 95 kW at PF 0.95. The exact figure depends entirely on the power factor of the load you connect, so check the generator's rated PF on its nameplate before assuming a number.
Can kW ever be higher than kVA?+
No, kW can never exceed kVA in a real circuit. Power factor is capped at 1.0, and since kW equals kVA times PF, the result can only equal or fall below the kVA figure.
Does a higher power factor mean more usable kW?+
Yes, a higher PF always increases the real power delivered for the same kVA rating. Raising PF from 0.8 to 0.95 on a 50 kVA source lifts usable output from 40 kW to 47.5 kW without changing the equipment.
What PF should I use if I don't know the load's actual power factor?+
0.8 is the standard assumption for mixed commercial and industrial loads when no nameplate data is available. Motor-heavy loads run closer to 0.7-0.75, while lighting and electronics-heavy loads often sit at 0.9 or higher.
Why is my generator's kW rating lower than its kVA rating?+
Because the kW figure already accounts for the manufacturer's assumed power factor, usually 0.8. A 62.5 kVA generator rated at 50 kW simply reflects 62.5 × 0.8, not a design flaw.
Is the kVA to kW formula the same for three-phase generators?+
Yes, the kW = kVA × PF relationship holds for single-phase and three-phase machines alike. Phase count and voltage only matter if you're also solving for current, not for this power conversion.
What happens if I load a generator past its kW rating but stay under its kVA rating?+
The generator can still overheat, because engine and alternator thermal capacity are tied to kVA, not kW. Staying under the kVA limit protects the windings; a low PF at high kVA still produces full heat for less usable kW.
Do UPS systems use the same kVA to kW conversion?+
Yes, UPS capacity follows the identical formula. A 10 kVA UPS rated at PF 0.9 supports 9 kW of connected IT load, which is why datasheets list both figures side by side.