VA to Watts Calculator
Convert volt-amps (apparent power) to watts (real power) at a given power factor. The result is a load's real power draw, not a UPS or power supply's output capacity. UPS watt ratings are set independently by the manufacturer and are often well below the VA figure times the load's PF, so size a UPS against both its published VA rating and its published watt rating, not against this formula.
What Is VA to Watts?
VA (volt-amps) measures a load's apparent power, the total power it pulls from the circuit, set by voltage times current. Watts measures real power, the portion of that apparent power that does useful work. The gap between them is the load's power factor, so Watts = VA × PF converts a load's apparent power to its real power at a given PF. It is a load-side calculation. It does not tell you the watt output of a UPS or power supply feeding that load, which is a separate manufacturer specification.
The Formula
Power factor ranges from 0 to 1.0. Resistive loads (heaters, incandescent bulbs) have PF 1.0, so a load's watts equal its VA. Motors run at PF 0.80-0.85. Computers without active power factor correction run at PF 0.60-0.70; modern computers with PFC power supplies run closer to 0.95-1.0. The lower the load's PF, the fewer real watts the load draws for the same apparent-power VA figure.
How VA vs Watts Affects UPS and Power Supply Sizing
UPS units and power supplies publish two independent ratings set by the manufacturer: a VA rating and a watt rating. Both are separate specs, and neither can be derived from the other using Watts = VA × PF. Older UPS designs assumed a load PF around 0.6 and published watt ratings well below their VA numbers (for example, 1000 VA / 600 W). Modern UPS units often publish watt ratings equal to their VA ratings because they are designed for high-PF computer loads with active power factor correction (for example, 1500 VA / 1500 W). You cannot tell from the VA rating alone.
To size a UPS for a load you need to do two independent checks against the manufacturer's spec sheet:
- Compute the load's apparent power in VA and make sure it does not exceed the UPS's VA rating.
- Compute the load's real power in watts (Watts = VA × PF) and make sure it does not exceed the UPS's watt rating.
The load has to fit under both ratings independently. The Watts = VA × PF formula only helps with check (2): it gives you the load's real power at a given PF. It does not predict the UPS's watt ceiling and should never be used to infer UPS output capacity from a VA rating.
Quick Results Table
| VA | PF 0.65 | PF 0.80 | PF 0.85 | PF 0.95 | PF 1.0 |
|---|---|---|---|---|---|
| 100 VA | 65W | 80W | 85W | 95W | 100W |
| 200 VA | 130W | 160W | 170W | 190W | 200W |
| 500 VA | 325W | 400W | 425W | 475W | 500W |
| 750 VA | 487.5W | 600W | 637.5W | 712.5W | 750W |
| 1,000 VA | 650W | 800W | 850W | 950W | 1,000W |
| 1,500 VA | 975W | 1,200W | 1,275W | 1,425W | 1,500W |
| 2,000 VA | 1,300W | 1,600W | 1,700W | 1,900W | 2,000W |
| 3,000 VA | 1,950W | 2,400W | 2,550W | 2,850W | 3,000W |
| 5,000 VA | 3,250W | 4,000W | 4,250W | 4,750W | 5,000W |
| 10,000 VA | 6,500W | 8,000W | 8,500W | 9,500W | 10,000W |