VA to Watts Calculator

Apparent power and real power

Every AC circuit carries two kinds of power. Apparent power, in volt-amps, is voltage multiplied by current — the total electrical loading the source has to handle. Real power, in watts, is the part that actually does work: heat, light, torque. The two are equal only for a purely resistive load. Anything with a motor winding or a switch-mode power supply draws current that’s partly out of phase with the voltage, so its apparent power runs higher than its real power.

The number that connects them is the power factor. It’s the ratio of watts to VA, always between 0 and 1. Get it wrong and you undersize a circuit or overload a UPS — the classic mistake being to assume a “1000 VA” UPS can run 1,000 watts of load when many older units top out near 600 W.

The VA to watts formula

is real power in watts, is apparent power, and is the power factor. The calculator also returns reactive power, the third side of the power triangle:

with in volt-amps reactive (VAR). The three relate as .

Worked example

The calculator’s defaults are 1,000 VA at a power factor of 0.8.

Real power:

Reactive power:

So the load does 800 W of work while 600 VAR circulates without being consumed. Check the triangle: VA, which matches the input.

VA to Watts Calculator worked example diagram — A visual read of the worked example above — the same numbers the calculator returns for its default inputs.

VA to watts by power factor

Apparent power	PF 1.0	PF 0.9	PF 0.8	PF 0.6
500 VA	500 W	450 W	400 W	300 W
1,000 VA	1,000 W	900 W	800 W	600 W
1,500 VA	1,500 W	1,350 W	1,200 W	900 W
3,000 VA	3,000 W	2,700 W	2,400 W	1,800 W

Modern computer power supplies use active power-factor correction and sit near 0.95 to 1.0. Motors, older linear supplies, and lightly loaded transformers pull the figure down toward 0.6 to 0.8.

What the result means for equipment

The watts figure is the real power the load consumes and what a utility meter records. The VA figure is what the source, its wiring, and any UPS or transformer in the path must be rated to carry. Size the supply from VA; understand the actual work from watts. On a UPS spec sheet, both limits are listed separately — you can’t exceed either.

Common mistakes

Reading a UPS’s VA rating as its watt rating. Check the watt figure too.
Using power factor 0.8 for a resistive heater. It’s 1.0; watts equal VA.
Treating reactive power as wasted energy. It burns no fuel, but it occupies conductor and transformer capacity the whole time it flows.

For the reverse direction, use the watts to kVA calculator. For the kilowatt scale, see VA to kW, and for current, VA to amps.

Frequently Asked Questions

What is the difference between VA and watts?+

VA (volt-amps) is apparent power — voltage times current. Watts is real power — the part that does useful work. The ratio between them is the power factor, which reflects the phase shift between voltage and current in an AC circuit.

How many watts is 1000 VA?+

At the default power factor of 0.8, 800 W. At unity power factor, the full 1,000 W. At 0.6 — a typical older UPS — only 600 W. This is why a '1000 VA' UPS often can't run a 900 W load.

What is power factor and why does it matter?+

It's the ratio of watts to VA, from 0 to 1. A value of 1 means every volt-amp does work. It matters because equipment must be rated for the full VA even when the watts are lower, and utilities may bill a penalty for a poor power factor on large services.

How do I find the power factor of my device?+

The nameplate often lists both VA and watts; divide watts by VA. For typical loads: resistive heaters near 1.0, computers without power-factor correction around 0.6 to 0.75, motors 0.7 to 0.9 depending on load.

Can watts ever be higher than VA?+

No. Real power is always equal to or less than apparent power. They're equal only at a power factor of 1.

What is the reactive power the calculator also shows?+

It's the VAR figure — the part of the apparent power that shuttles in and out of the load's magnetic or electric field without being consumed. It's found from VA × √(1 − PF²), and it's the third side of the power triangle alongside watts and VA.