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How Many Watts Does a Window AC Use? Watts by BTU, Amps, and Backup Power
A window air conditioner uses about 440 to 990 watts for the common 5,000 to 12,000 BTU sizes, or roughly 4 to 9.3 amps at 115 volts. A 5,000 BTU unit draws about 440 watts, an 8,000 BTU about 660 watts, and a 12,000 BTU about 990 watts at full cooling, based on LG's ratings. Newer variable-speed units average less once the room cools down.
Window AC watts and amps (manufacturer ratings)
Here is what LG lists for three of its window units:
| Model | Cooling capacity | Watts (cooling) | Rated amps | Volts |
|---|---|---|---|---|
| LG LW5016 | 5,000 BTU | 440 W | 4.1 A | 115V |
| LG LW8016ER | 8,000 BTU | 660 W | 6.2 A | 115V |
| LG LW1216ER | 12,000 BTU | 990 W | 9.3 A | 115V |
Source: LG product specifications. These are full cooling ratings, so use them to size a generator, inverter, or power station.
Window AC watts by BTU (ENERGY STAR data)
Every ENERGY STAR certified window unit on the current list has a variable-speed compressor, which slows down once the room is cool. This table shows the average watts implied by each size's efficiency rating (BTU / CEER), across 513 certified window models:
| Cooling capacity | Average watts (range) | Typical | kWh per year | Volts |
|---|---|---|---|---|
| 5,000 BTU | 347 to 382 W | 347 W | 260 | 115V |
| 6,000 BTU | 375 to 438 W | 438 W | 329 | 115V |
| 8,000 BTU | 500 to 606 W | 533 W | 400 | 115V |
| 10,000 BTU | 625 to 704 W | 667 W | 500 | 115V |
| 12,000 BTU | 750 to 902 W | 800 W | 600 | 115V |
| 14,000 BTU | 875 to 952 W | 933 W | 700 | 115V |
| 18,000 BTU | 1,125 to 1,250 W | 1,200 W | 900 | 230V |
| 24,000 BTU | 1,739 to 1,890 W | 1,805 W | 1,353 | 230V |
Source: ENERGY STAR Certified Room Air Conditioners data set. Typical = median. The yearly kWh figures equal those average watts over 750 hours of use a year.
Why the two tables differ: the LG numbers are full-power cooling. The ENERGY STAR numbers are an average that includes the slower, part-load running a variable-speed unit does after the room cools. Size backup power for the full-power number; estimate your electric bill with the average.
Find your own number: the label on the side of the unit, or its spec sheet, lists cooling watts and amps.
How many amps does a window AC use?
About 4 to 9.3 amps at 115V for 5,000 to 12,000 BTU units, based on LG's ratings. That fits a standard 15 amp outlet, but a 12,000 BTU unit at 9.3 amps leaves little room for anything else on the same circuit. The large 18,000 and 24,000 BTU units in the ENERGY STAR list run on 230V and need a 240V circuit.
How much electricity does a window AC use per day?
Watts x hours / 1,000 = kWh per day. A variable-speed 8,000 BTU unit averaging 533 watts for 8 hours uses about 4.3 kWh, roughly 73 cents at 17 cents per kWh. At LG's full 660 watt rating the whole time, it would be 5.3 kWh.
Can a portable power station run a window AC?
Yes, for smaller units. Run time at full cooling power, with nothing else plugged in:
| Power station | Capacity / output | 5,000 BTU (440 W) | 8,000 BTU (660 W) | Price |
|---|---|---|---|---|
| Jackery Explorer 1000 v2 | 1,070 Wh / 1,500 W | About 2.2 hours | About 1.5 hours | From $499 |
| Jackery Explorer 2000 v2 | 2,042 Wh / 2,200 W | About 4.2 hours | About 2.8 hours | From $899 |
| Jackery HomePower 3000 | 3,072 Wh / 3,600 W (7,200 W surge) | About 6.3 hours | About 4.2 hours | From $1,349 |
Hours = capacity x 0.9 / watts. Capacity, output, and surge are from each product page. These assume full-power cooling the whole time, so a unit that cycles or slows down runs longer. Older single-speed units pull extra current for a moment when the compressor starts, so test yours on the station before you count on it. Browse all portable power stations.
What size generator do you need for a window AC?
A 115V window unit is an easy load for most home backup generators. In-stock portable generators:
- DuroMax XP5500HX: 5,500 starting / 4,500 running watts on gasoline, CO alert shutoff. Runs a 12,000 BTU window unit (990 W) plus a fridge and lights. $629
- DuroStar DS8000iX: 8,000 starting / 6,500 running watts, inverter power, L14-30 outlet. Room for two or three window units plus essentials. $999
Running central air instead? See What Size Generator Do You Need to Run a House? Going solar? See How Many Solar Panels to Run an Air Conditioner? For the whole picture, read How Many Watts Does a House Use?
Need help sizing? Call 1-888-855-7286. Send us the BTU and amps from your AC's label and we will match you to a power station or generator.
Window AC wattage FAQ
How many watts does a window AC use? About 440 to 990 watts at full cooling for 5,000 to 12,000 BTU units, per LG's ratings. Variable-speed ENERGY STAR units average about 347 to 800 watts for the same sizes.
How many watts does a 5,000 BTU air conditioner use? About 440 watts at full cooling (LG LW5016) and about 347 watts on average for variable-speed ENERGY STAR models.
How many watts does an 8,000, 10,000, or 12,000 BTU AC use? Variable-speed ENERGY STAR models average about 533, 667, and 800 watts. LG rates its 8,000 BTU at 660 W and its 12,000 BTU at 990 W at full cooling.
How many amps does a window AC use? About 4.1 amps for a 5,000 BTU unit, 6.2 amps for 8,000 BTU, and 9.3 amps for 12,000 BTU at 115V, based on LG's ratings.
Can a generator run a window AC? Yes. A 4,500 running watt generator runs a 12,000 BTU window unit with room for a fridge and lights.