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VA to Watts Calculator
Volt-amps are what a UPS, a generator or an inverter is rated at; watts are what your equipment actually receives.
Apparent power to real power. The difference is the power factor.
Watts = VA × Power factor
To convert VA to watts, multiply the volt-amps by the power factor of the load. At the 0.8 power factor most UPS and generator nameplates assume, a 1,000VA unit delivers 800 real watts. Feed a purely resistive load such as a heater and the power factor is 1.0, so 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.
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.
The mistake almost everyone makes. Assuming a 1,500VA UPS will hold a 1,500W load. It will not. Depending on the model it is rated between 900W and 1,350W, and that watt figure is printed on the unit beside the VA figure. When a manufacturer gives you both numbers, use the printed watts. The 0.8 rule is a fallback for when you have only one of them.
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 when you have nothing better, because it is the convention behind most UPS and generator ratings and it errs low. Use 0.6 for an older UPS or a motor-heavy load, and 0.9 to 1.0 for modern electronics and anything purely resistive.
| Apparent power | PF 0.6 | PF 0.8 (default) | PF 0.9 | PF 1.0 |
|---|---|---|---|---|
| 100VA | 60W | 80W | 90W | 100W |
| 350VA | 210W | 280W | 315W | 350W |
| 500VA | 300W | 400W | 450W | 500W |
| 650VA | 390W | 520W | 585W | 650W |
| 750VA | 450W | 600W | 675W | 750W |
| 1,000VA | 600W | 800W | 900W | 1,000W |
| 1,200VA | 720W | 960W | 1,080W | 1,200W |
| 1,500VA | 900W | 1,200W | 1,350W | 1,500W |
| 2,000VA | 1,200W | 1,600W | 1,800W | 2,000W |
| 2,200VA | 1,320W | 1,760W | 1,980W | 2,200W |
| 3,000VA | 1,800W | 2,400W | 2,700W | 3,000W |
| 5,000VA | 3,000W | 4,000W | 4,500W | 5,000W |
| 10,000VA | 6,000W | 8,000W | 9,000W | 10,000W |
Kilovolt-amps move the decimal and nothing else: a 5kVA generator is 5,000VA, or 4,000W at the standard 0.8. 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.
Why this conversion matters for portable power
Portable power stations are sold in watts and watt-hours. UPS units, standby generators and many off-grid inverters 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 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.
A watt rating assumes a well-behaved load. An inverter is limited by current as well as by real power, so a low-power-factor load can trip a 1,000W unit while the wattmeter still reads under 1,000W. Read a continuous watt rating as the figure at or near unity power factor, and leave headroom for motors.
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.
| Load | Typical power factor | Notes |
|---|---|---|
| Kettle, toaster, resistive heater | 1.0 | Pure resistance; VA and watts are identical |
| Incandescent bulb | 1.0 | Also pure resistance |
| Modern PC or server supply with active PFC | 0.95–0.99 | Correction is built in and works well |
| Older PC supply with no PFC | 0.6–0.7 | The origin of the 0.6 UPS convention |
| Laptop and phone chargers | 0.5–0.95 | Wide spread, small numbers either way |
| LED lighting | 0.5–0.9 | Cheap drivers sit at the bottom of the range |
| Refrigerator or freezer compressor | 0.6–0.8 | Worse at startup than when running |
| Air conditioner, pump, power tool | 0.7–0.9 | Induction motors; size for surge separately |
| Microwave oven | 0.6–0.9 | Depends heavily on the transformer design |
| Anything running on DC | 1.0 | No phase shift exists on DC |
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 0.8 and treat 1,200W as an optimistic ceiling.
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.
| Real power | Apparent power at PF 0.8 | Apparent power at PF 0.9 |
|---|---|---|
| 300W | 375VA | 333VA |
| 500W | 625VA | 556VA |
| 800W | 1,000VA | 889VA |
| 1,000W | 1,250VA | 1,111VA |
| 1,200W | 1,500VA | 1,333VA |
| 1,500W | 1,875VA | 1,667VA |
| 2,000W | 2,500VA | 2,222VA |
| 3,000W | 3,750VA | 3,333VA |
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
How do I convert VA to watts?
Multiply the volt-amps by the power factor of the load. With no better information use 0.8, so a 1,000VA rating becomes 800W. If the device prints both a VA and a watt rating, use the printed watts: that figure is the manufacturer’s own rather than a rule of thumb.
Is 1000VA the same as 1000 watts?
Only for a purely resistive load such as a kettle or a heater, where the power factor is 1.0. For everything else the watts are lower, typically 600W to 900W depending on what is plugged in. On DC, volt-amps and watts genuinely are the same number.
How many watts is a 1500VA UPS?
Between 900W and 1,350W depending on the model: 900W at a power factor of 0.6, 1,200W at 0.8 and 1,350W at 0.9. The exact figure is printed beside the VA rating. Both limits apply at once, so the UPS stops at whichever it reaches first.
What power factor should I use if I do not know it?
Use 0.8. It is the convention behind most UPS and generator nameplates, and it under-estimates rather than over-estimates the watts available, which is the safe direction. Drop to 0.6 for an older UPS or a motor-heavy load, and use 0.95 or above for electronics with active power-factor correction.
Why are UPS units and generators rated in VA instead of watts?
Because their real limit is current, not useful output. Transformers, wiring and switching devices heat up according to the current they carry, whether or not it does any work. Volt-amps describe that limit honestly; watts describe what the connected equipment receives.
Does the VA to watts conversion apply to batteries and solar panels?
No. Batteries, solar panels and DC circuits have no power factor, so volt-amps and watts are identical there. It matters only on the AC side: after the inverter in a power station, or at the output of a UPS, a generator or a grid-tie system.
Can I run a 1000W appliance on a 1500VA inverter?
Only if the inverter’s watt rating is 1,000W or more, which at 1,500VA means a power factor of 0.67 or better. Check the printed watt figure first, then the surge rating: a compressor drawing 1,000W while running can demand several times that at startup.
Next step. A watt figure on its own only sizes the inverter. To size the battery behind it, our power station sizing guide turns a list of loads into a capacity number.