VA to Watts Calculator

To convert VA to watts, multiply the volt-amps by the power factor of the load. Many kVA-rated inverters and three-phase commercial generators are rated at a 0.8 power factor, so a 1,000VA unit delivers 800 real watts; consumer desktop UPS units are usually rated nearer 0.6–0.67, so a 1,000VA desktop UPS is typically 600–670W. Single-phase home generators are normally rated at 1.0, so their kVA and watt figures match, and a purely resistive load such as a heater also runs at 1.0: 1,000VA is a full 1,000W.

The formula, and what each term means

Three quantities are involved, and they are genuinely different things, not three names for one.

• Volt-amps (VA) are apparent power: circuit voltage multiplied by the current flowing through it. It is what the cable, the breaker and an inverter’s output stage must carry, whether or not that current achieves anything.
• Watts (W) are real power: the share that becomes heat, light or motion. It is what your meter bills you for and what drains a battery.
• Power factor (PF) is the ratio between them, a number between 0 and 1: watts divided by volt-amps, nothing more complicated. The Department of Energy’s power factor fact sheet defines it the same way and names inductive loads such as motors and transformers as the cause of a low one.

On alternating current, voltage and current do not always rise and fall together. An induction motor pulls current out of step with the voltage; a cheap switch-mode supply pulls it in distorted spikes. Either way some of the current does no work, and the power factor is the fraction that does. On DC there is no phase shift, so the power factor is 1 and the units are interchangeable.

VA to watts conversion table

Power factor is the only variable here, so the table gives four of them. Voltage does not appear at all: 120V, 230V and 240V produce identical answers. Use the 0.8 column for a kVA-rated inverter or a three-phase generator that prints no watt figure, because 0.8 is the convention behind many of their ratings. A single-phase home generator is normally rated at 1.0, so read it from the last column: its kVA figure is already its watts. Use 0.6 for a consumer desktop UPS whose label gives no watt figure (most are rated 0.6–0.67) or for a motor-heavy load, and 0.9 to 1.0 for modern electronics and anything purely resistive. Some online and pure-sine UPS units are rated at 0.9–1.0, but only the printed watt figure tells you which.

Kilovolt-amps move the decimal and nothing else: a 5kVA three-phase generator is 5,000VA, or 4,000W at the standard 0.8, while a 5kVA single-phase generator rated at 1.0 is a 5,000W machine. If a nameplate quotes both figures, divide the watts by the volt-amps to recover the manufacturer’s own power factor and use that instead.

Real ratings from UPS, generator and inverter makers

The table above runs on conventions. These are the figures makers publish for their own products, taken from each maker’s spec page or sheet. Where a maker gives both numbers, the power factor is simply the watts divided by the volt-amps.

Five 1,500VA UPS units

Same VA rating, watts from 865W to 1,500W. The BR1500G sits just under the 0.6 rule of thumb, which is why a printed watt figure beats any assumption.

Generators and inverters

The Honda shows what the 0.8 shortcut does to a single-phase generator: 1.8kVA × 0.8 is 1,440W, 20% under the 1,800W Honda prints for the same machine. The 0.8 convention belongs to three-phase commercial sets, where the SD050’s 63kVA headline is its 50kW divided by 0.8, and to inverters like the Victron, which also gives up output as it warms. One limit still applies to a generator rated at 1.0: current. Generac’s 91.7A at 240V is 22,000VA, so a motor load at a 0.8 power factor reaches that current at about 17,600W.

Why this conversion matters for portable power

Portable power stations are sold in watts and watt-hours. UPS units, many off-grid inverters and some generators are sold in VA or kVA. Anyone shopping for outage backup compares the two, which means doing this conversion whether they notice or not.

Replacing a UPS with a power station

A 1,500VA desk UPS sounds far larger than a 1,000W power station. It is usually smaller. At a 0.6 power factor that UPS is a 900W device holding a load for minutes; the power station is a 1,000W device holding it for hours. Compare watts with watts, never with VA. Browse power stations on continuous output, and for anything panel-level start with home battery backup instead.

Sizing against an inverter you already own

If the inverter in your RV, van or cabin is stamped in VA, convert before you add up appliance loads, because appliance labels are in watts. Mixing the two units is how people end up 20% over the limit and puzzled by a shutdown that looks unprovoked.

Solar, where the ratings run both ways

Grid-tie inverters and microinverters are held near unity power factor by connection rules, so their output rating in VA and in watts is usually the same number. Balcony systems are the trap: the hardware may be specified in VA while the export limit that applies to it is written in watts. Our introduction to plug-in solar covers the rest.

After that the rest is arithmetic: watts against the continuous output rating, watts multiplied by hours against the capacity in watt-hours. The power station finder filters on both at once, and the comparison tool puts candidates side by side.

Power factor by device type

If you can measure the power factor, measure it: most plug-in energy monitors display it directly, and one reading beats any assumption here. Failing that, use these ranges. They are general engineering figures, not specifications for any particular product.

The pattern without the table: heat is 1.0, motors around 0.8, cheap electronics unpredictable enough to be worth measuring.

Worked examples, and going the other way

A 1,500VA UPS. If the label also says 900W, the power factor is 0.6 and 900W is the answer. If it says 1,350W, the power factor is 0.9. If it says nothing, assume 0.6 and plan on 900W; 0.8 would overstate most desktop units.

A 3kVA off-grid inverter. 3,000VA at 0.8 is 2,400W of real power. Compare the appliance labels you intend to run with 2,400, not with 3,000.

Turning watts into runtime. VA contains no time, so it says nothing about how long anything lasts. Convert first, then divide capacity by draw. A 300W load on a 1,000Wh power station, allowing 15% for inverter losses, has about 850Wh to work with: 850Wh ÷ 300W ≈ 2 hours 50 minutes. The watts to kWh calculator handles the energy side.

Watts back to VA

Divide rather than multiply. This is the direction you need when appliance labels are in watts and the hardware is rated in VA.

Breakers, cables and the 80 percent rule

Wiring responds to current, which puts it on the VA side of this conversion rather than the watts side. A 120V, 15A circuit carries 1,800VA. For a continuous load, meaning anything drawing for three hours or more, US practice derates that by 80% to 1,440VA; a 20A circuit gives 2,400VA, or 1,920VA continuous.

Those ceilings are in volt-amps, which is the point. A 1,440VA load at a 0.7 power factor is barely 1,000W of useful output, and the breaker does not care that the rest achieved nothing. Working from a current reading instead, the amps to watts calculator covers that step.

Frequently asked questions