kW to kVA Calculator
Convert kW to kVA using the power factor. Live calculator for generator and UPS sizing with worked examples.
Common conversions
| Input | Result |
|---|---|
| 5 kW @ PF 1.0 | 5 kVA |
| 10 kW @ PF 0.9 | 11.11 kVA |
| 18 kW @ PF 0.75 | 24 kVA |
| 25 kW @ PF 0.8 | 31.25 kVA |
| 40 kW @ PF 0.85 | 47.06 kVA |
| 60 kW @ PF 0.9 | 66.67 kVA |
| 100 kW @ PF 0.95 | 105.26 kVA |
The math behind it
- kVA = kW / PF
- kVA = 18 / 0.75
- kVA = 24
Everything you need to know
Converting kW to kVA answers the question every equipment buyer eventually asks: if I know how much real power my load needs, how big a generator, UPS, or transformer do I actually have to buy? Because apparent power is always equal to or larger than real power, the kVA figure is the number that determines equipment size, not the kW figure alone.
How the kW to kVA formula works
Kilowatts measure real power, the portion of the electrical supply that actually does work: spinning a motor shaft, producing light, or generating heat. Kilovolt-amps measure apparent power, the total combination of voltage and current the source has to supply, including the reactive portion that motors, transformers, and switch-mode supplies pull without converting it into usable output. Dividing kW by PF undoes the multiplication that produced kW from kVA in the first place, so it always pushes the number back up (or leaves it unchanged at PF 1.0). That's why kVA is never smaller than kW, and why a lower power factor always demands a larger, more expensive piece of equipment for the same amount of real work.
Why generators, transformers, and UPS units are sized in kVA
Every piece of power equipment has a hard current limit set by its windings, conductors, and cooling system, and that limit is defined in amps and volts, which combine into kVA, not kW. A manufacturer publishing a kW rating alone would have to guess your load's power factor, and guessing wrong in either direction either strands capacity or sells you an underpowered unit. Publishing a kVA rating sidesteps that guesswork: you take your known kW demand, divide by your own load's real PF, and compare the result against the equipment's kVA nameplate. That's why generator, UPS, and transformer catalogs are organized by kVA size steps rather than kW, and why RFPs for standby power almost always specify a kVA figure as the minimum requirement.
Worked scenario: sizing a UPS for a server room
A facilities manager measures an 18 kW real-power draw from a row of server racks, and the switch-mode power supplies in that equipment run at PF 0.75, lower than a typical office because of the harmonic current the supplies pull. Dividing 18 kW by 0.75 gives 24 kVA of required apparent-power capacity. Buying a UPS rated for exactly 18 kVA, on the assumption that kW and kVA are close enough, would leave the unit 6 kVA short and trigger overload alarms the first time the racks hit full load. Sizing to the correct 24 kVA figure, with some added headroom for future rack additions, keeps the UPS comfortably inside its rated capacity.
Common applications
Take the building's worst-case kW demand, divide by 0.8 PF, and shop for a genset whose kVA rating exceeds that figure with at least 20% headroom.
Inverter and UPS specs are stated in VA. Convert your IT or telecom kW load to kVA so you don't buy a unit that trips before it reaches its watt rating.
Transformers are stocked in standard kVA sizes: 15, 25, 37.5, 50, 75, 112.5, 150. Convert anticipated kW to kVA to pick the next size up.
Utilities size new service drops in kVA. Submitting your real kW demand converted to kVA, rather than the raw kW figure, gets an accurate quote on the first pass.
Common mistakes
Generators and transformers must handle apparent power. Using PF = 1 understates kVA and produces equipment that overheats under real loads.
Capacitor banks produce leading PF, motors produce lagging PF, and they partially cancel. Measure the net PF at the service point before sizing.
A calculated kVA result smaller than the input kW figure means a PF greater than 1.0 was entered by mistake, which is not physically possible.
Steady-state kVA from this formula doesn't cover motor starting current, which can spike to 6-8 times running current for a few seconds and briefly demand far more kVA.
Frequently asked questions
Why is kVA bigger than kW?+
Because apparent power includes the reactive component that real power doesn't. Dividing kW by a power factor below 1.0 always produces a larger number, and the two are equal only when PF is exactly 1.0.
What is the standard generator PF used for sizing?+
0.8 lagging is the industry-standard assumption for diesel and gas gensets. Always check the nameplate first since some modern units are rated at 0.9 or unity.
How many kVA do I need for a 10 kW load?+
12.5 kVA at PF 0.8, or 11.11 kVA at PF 0.9. Divide your known kW figure by the load's actual power factor, not an assumed one, whenever nameplate data is available.
Does a lower power factor increase the kVA I need?+
Yes, a lower PF always increases the required kVA for the same kW load. Dropping PF from 0.9 to 0.7 on a 20 kW load raises the requirement from 22.2 kVA to 28.6 kVA.
Can kVA ever equal kW exactly?+
Yes, when the power factor is exactly 1.0, which happens with purely resistive loads like electric heaters or incandescent lighting. Most real-world loads sit below 1.0, so kVA usually exceeds kW.
Should I add margin on top of the calculated kVA?+
Yes, most engineers add 15-25% headroom above the calculated kVA figure. That margin covers future load growth, inrush current, and PF drift under partial loading.
Is the kW to kVA formula different for single-phase versus three-phase?+
No, the kVA = kW / PF relationship is identical regardless of phase count. Phase and voltage only enter the calculation if you also need to solve for current.
What happens if I size a transformer using PF 1.0 by mistake?+
The transformer will be undersized in kVA for any load with a real PF below 1.0. A transformer sized for 50 kVA at an assumed PF of 1.0 will actually need to supply 62.5 kVA to serve a 50 kW load at PF 0.8, exceeding its rating.
Do inverters and solar systems use this same conversion?+
Yes, inverter output capacity is rated in kVA for the same thermal reasons as generators. A 5 kW solar inverter with PF 0.95 output still needs roughly 5.26 kVA of downstream wiring and breaker capacity.