kVA to Kilowatts Calculator
Why does a UPS or standby generator carry a kVA number on its nameplate instead of a plain kW figure? Because the hardware inside it is limited by current and voltage, not by how much of that current turns into usable work, and answering that question is also the fastest way to size the unit correctly, since the kVA rating alone overstates the real power it can deliver to anything other than a perfect, unity-power-factor load.
kW = 60 × 0.8 = 48.00 kW
Apparent power versus real power
kVA is apparent power, the product of voltage and current, with no accounting for how much of that current is doing real work. kW is real power, the portion that actually runs a load. The two are only equal when the power factor is 1.0, a condition purely resistive equipment can meet but almost nothing else does. A UPS, a generator or a transformer sits between an unpredictable mix of downstream loads and a fixed physical limit on the current its internal wiring can carry, so the manufacturer rates it in the unit that describes that limit directly: kVA.
That is also why a kVA figure on its own cannot tell a buyer how much real power a UPS can deliver. Two units with an identical 60 kVA rating can supply very different amounts of usable kW depending on the power factor of whatever load ends up connected, which is the gap the conversion below closes.
That gap isn't fixed, either. A UPS backing mostly IT load sitting close to unity power factor can realize nearly its full kVA rating as usable kW, while the same UPS supporting older mechanical equipment or variable-frequency drives might only turn 70-80% of its kVA figure into real power. That's part of why 0.8 shows up so often on UPS and generator nameplates. It's a conservative middle ground manufacturers pick so the printed kW rating holds up across a reasonably wide mix of real-world loads, not a figure every connected load actually runs at.
The formula
Real power is apparent power scaled down by the power factor: kW = kVA × PF. Power factor is a ratio between 0.01 and 1.00, so multiplying by it can only shrink the apparent-power figure or leave it unchanged, never grow it. Reversing the formula, kVA = kW / PF, is the calculation an installer runs when a known kW load needs to be checked against a UPS or generator's kVA capacity before it's connected.
Nameplates that only print a kVA figure typically assume a stated power factor, commonly 0.8 for UPS and generator equipment, to arrive at the kW rating printed alongside it. Swapping in the load's actual power factor instead of that assumed figure gives a more accurate real-power number for a specific installation.
A UPS with a built-in monitor, or a facility power meter reading the same circuit, can usually report the connected load's actual power factor directly. That measured figure is a more reliable input than an assumed 0.8 whenever it's available. The assumed value is only a starting point for a rough capacity check on a spec sheet, not a substitute for what the equipment is really seeing once it's carrying a live load.
Worked example: sizing a 60 kVA UPS
60 kVA UPS nameplate rating, power factor 0.8 (a typical UPS/generator assumption).
- 1
Start from the formula
kW = kVA × PF
- 2
Substitute the nameplate values
kW = 60 × 0.8
- 3
Solve
kW = 48 kW
- 4
Compare against the critical load
48 kW is the ceiling to check the facility's real-power draw against, not 60 kVA.
This is general reference arithmetic. A UPS or generator's real-world usable output can also be limited by its own kW rating, temperature, altitude and load transients. A licensed electrician confirms the final sizing for a real installation.
Common UPS and generator sizes, kVA to kW
Power factor 0.8, the typical assumption printed on UPS and standby generator nameplates. A unit running at a different power factor delivers a different kW figure for the same kVA rating.
| Nameplate rating | Real power at PF 0.8 |
|---|---|
| 10 kVA | 8 kW |
| 20 kVA | 16 kW |
| 30 kVA | 24 kW |
| 45 kVA | 36 kW |
| 60 kVA | 48 kW |
| 80 kVA | 64 kW |
| 100 kVA | 80 kW |
| 150 kVA | 120 kW |
Reference estimates only, not measured values. Confirm any real unit against its own nameplate and actual load power factor.
Sizing equipment rated in kVA
Questions
kVA to kilowatts FAQ
Sizing questions that come up when a UPS, generator or transformer nameplate has to be checked against a real power-factor load.
Why is a UPS or generator rated in kVA instead of kW?
Because the transformers, alternator windings and switching components inside a UPS or generator are limited by current and voltage, not by how much of that current does useful work, and current times voltage is exactly what kVA measures. The kW figure depends on the power factor of whatever gets plugged in later, which the manufacturer cannot know in advance. Rating the unit in kVA describes what its internal hardware can physically carry regardless of the load attached to it.
What happens if a UPS is loaded near its full kVA rating at a low power factor?
The UPS can still be within its kVA limit while delivering noticeably less real power than its kVA number implies, because kW = kVA × PF and a low PF shrinks that product. A 60 kVA UPS running a load at PF 0.6 tops out at 36 kW of real power, not 48 kW, so a facility that sized its critical load assuming a higher power factor can find itself short of usable capacity even though the UPS display shows headroom on the kVA side.
Why can a generator's usable kW output be less than its kVA rating suggests?
A generator's kVA rating describes the alternator's current-carrying limit, while its kW rating (often listed separately, or implied at a stated power factor) describes the real power the engine and alternator are actually built to sustain. A genset nameplate showing both figures at PF 0.8 already reflects this gap. The kW number is the one that matters for sizing against a facility's actual real-power demand, and treating the kVA number as the usable output overstates what the machine can deliver as general reference.
Is kVA or kW the number to check against a UPS's real load?
Both, separately: kVA has to stay under the UPS's apparent-power limit, and kW has to stay under its real-power limit, and a load with a low power factor can hit one ceiling well before the other. A UPS sized only by comparing its kVA rating to a load's kW draw can look oversized on paper while actually running close to its current limit, since the missing power-factor conversion hides how much apparent power that load is really pulling.
How do transformer kVA ratings relate to this same kVA-to-kW conversion?
A distribution transformer is rated in kVA for the identical reason a UPS is: its windings and core are limited by current, not by the power factor of whatever load ends up connected downstream. The same kW = kVA × PF relationship applies: a 45 kVA transformer supplying a load at PF 0.8 is delivering 36 kW of real power, and confirming that figure against the connected equipment's actual demand is a job for a licensed electrician on any real installation.
Does a higher power factor always mean more usable kW from the same kVA rating?
Yes: for a fixed kVA rating, kW rises in direct proportion to power factor, up to the theoretical ceiling of PF 1.0 where kW and kVA become equal. That same 60 kVA UPS delivers 48 kW at PF 0.8 but only 42 kW at PF 0.7, which is why a UPS spec sheet showing a kW figure always states the power factor it assumed to get there.