What does your air conditioner cost to run?
Estimated cost per hour of running
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Estimate: watts = Btu/h ÷ efficiency rating, then × hours × your rate. For central and mini-split units we use SEER2 in the same simple division; SEER2 is a seasonal average, so a real day can draw more (very hot) or less (mild). Window units use CEER or EER directly. State rates are average residential prices (EIA, July 2026); your bill's all-in rate is more accurate.
How the math works
Power draw in watts is the cooling capacity in Btu/h divided by the efficiency rating, which is measured in Btu per watt-hour. Divide by 1,000 for kilowatts, multiply by the hours the compressor runs, then multiply by your rate per kWh. For example, a 12,000 Btu/h window unit rated 14.7 CEER draws about 816 W, or about 15¢ an hour at the 18.31¢ US average.
For central air and mini-splits the same division uses the SEER2 rating. That is an approximation: SEER2 is a seasonal average, and the true draw on any one day depends on outdoor temperature, humidity and how hard the unit is working. We did not apply an EER conversion factor to SEER2, because the relationship varies by equipment, so the central and mini-split results are labelled estimates.
What this calculator assumes
- Starting values. The 14.7 CEER window unit and the 15.2 SEER2 central system are the reference efficiency levels used in our AC electricity cost per hour guide, which cites the Department of Energy. The 20 SEER2 mini-split is an illustrative choice; models vary widely.
- Rates. State rates are EIA average residential prices for July 2026. Your bill's all-in price per kWh, including delivery charges, is more accurate, so type it into the rate box if you know it.
- Cycling. Hours are compressor running hours. Enter fewer hours than the unit is switched on if it cycles.
- Not included. Fan-only time, demand charges, time-of-use pricing and any repair or maintenance costs.
Keep going
For the tables behind the defaults and the state-by-state hourly costs, read AC electricity cost per hour. To compare equipment, see mini-split vs central air cost and the mini-split cost calculator. To cut the bill itself, try how to lower your electric bill and annual HVAC maintenance cost. To price your whole home's electricity, use the electric bill estimator.
Frequently asked questions
How much does it cost to run an air conditioner per hour?
At the 18.31¢ US average residential rate (EIA, July 2026), our estimate is roughly 10 to 20¢ an hour for a window unit, about 43 to 49¢ for a 3-ton central system and about 9 to 11¢ for a one-zone mini-split. These are estimates from capacity divided by an efficiency rating, and they describe the compressor running continuously.
How do I find my air conditioner's Btu and efficiency rating?
Both are on the unit's nameplate or in its manual. Window units list Btu/h and an EER or CEER. Central and ductless systems list capacity in Btu/h or tons (1 ton = 12,000 Btu/h) and a SEER or SEER2 rating. Enter them as shown; do not convert between rating types.
Is the cost per month the same as running it 24 hours a day?
No. The hours field is for compressor running time. Once a room reaches the set temperature the compressor cycles off, so the compressor runs for fewer hours than the unit is switched on. Use a plug-in power meter on a window unit, or compare a hot month's kWh with a mild month's on your bill, to find the real figure.
Why does the calculator use SEER2 for central air and mini-splits?
SEER2 is the rating those units carry. It is a seasonal average across a range of outdoor temperatures, so dividing Btu/h by it is a simple approximation of average draw. On a very hot afternoon the unit can draw more, and in mild weather less, so treat the result as an estimate.
Will a bigger air conditioner cost more to run?
Per hour of running, yes: more Btu/h at the same efficiency means more watts. But an oversized unit is not a good deal, because ENERGY STAR warns an oversized room unit costs more to buy, wastes energy and does not cool better. Match capacity to the space.
