Turn a volt-ampere rating from a UPS, small transformer or equipment label into kilovolt-amperes.
Starting from an apparent-power rating instead? Use the main kVA to kW converter for any power factor.
Every diagram and table on this page updates with the calculator above.
The "k" prefix means a thousand, exactly as it does for grams or metres.
A 1,500 VA UPS is a 1.5 kVA UPS. Same machine, same capacity, different notation — manufacturers switch to kVA somewhere above 3,000 VA because the numbers get unwieldy.
Almost always VA, typically 350–3,000 VA, usually with a separate watt figure alongside.
Machine control circuits are specified in VA because contactor coils are rated in VA too.
Medical and audio isolation units sit in the 100–5,000 VA range.
LED and fluorescent drivers list VA input alongside their watt output.
The pattern is consistent: anything small enough that kVA would be an awkward fraction gets labelled in volt-amperes instead.
A UPS carries two ratings and your load has to respect both. The VA figure limits current through the inverter and the transfer switch; the watt figure limits the real power the battery and electronics can sustain.
You can use the full 900 W, but never the full 1,500 VA — the watt limit stops you first on almost any real load.
Standard ratings with the real power each supports at your chosen power factor.
| VA | Apparent power (kVA) | Real power (kW) |
|---|---|---|
| 100 VA | 0.1 | 0.09 |
| 250 VA | 0.25 | 0.225 |
| 400 VA | 0.4 | 0.36 |
| 500 VA | 0.5 | 0.45 |
| 650 VA | 0.65 | 0.585 |
| 750 VA | 0.75 | 0.675 |
| 1,000 VA | 1 | 0.9 |
| 1,500 VA | 1.5 | 1.35 |
| 2,000 VA | 2 | 1.8 |
| 3,000 VA | 3 | 2.7 |
| 5,000 VA | 5 | 4.5 |
| 10,000 VA | 10 | 9 |
| 15,000 VA | 15 | 13.5 |
| 20,000 VA | 20 | 18 |
Runtime depends on watts drawn and battery energy, not on the VA badge. A bigger VA number with the same battery buys you no extra minutes at all.
Use about 0.9 for inverter efficiency, and remember lead-acid capacity falls at high discharge rates.
| Load | Typical draw | Runtime on a 1.5 kVA / 900 W unit |
|---|---|---|
| Single desktop and monitor | 150 W | 20 – 30 min |
| Small network rack | 400 W | 7 – 10 min |
| Loaded to the watt limit | 900 W | 3 – 5 min |
Indicative only — always check the manufacturer runtime curve for the specific model.
Halving the load usually more than doubles the runtime, because lead-acid batteries deliver less of their rated capacity at high discharge currents.
Use a plug-in meter or the PDU reading, not the nameplate figures on the back of each device — nameplates are worst-case and wildly pessimistic.
Covers growth and keeps the UPS out of the top of its range, where efficiency and runtime both suffer.
Divide watts by the load power factor to get the apparent power the inverter must carry.
Confirm your figure sits under the unit VA rating and its watt rating.
Decide whether you need ride-through for brief dips or enough time for an orderly shutdown, then pick the battery to match.
29 calculators built on the same maths as the tool above. Each one has its own inputs, interactive diagrams and worked examples.
Common questions about converting va to kva.