How Much Electricity Does a Central AC Use per Month?

There is no single number: it depends on the size of the system, its rating and the hours it runs. Enter yours below, then see how each one changes the bill.

Last reviewed November 3, 2026. Written by the Team of Housenergy Calculator.

Sample numbers only, to show how it works. Replace them with yours.

Your price and your cooling season

State

Average residential price, 2024 annual average (EIA).

Price per kWh (dollars)

Filled from the state average. Replace it with the rate on your bill.

Days a year you cool

Days between the first and last day you run the air conditioning.

Your air conditioner

Capacity of one unit (Btu/h)

Listed in Btu per hour on the label or the box.

Efficiency rating (SEER2 or EER)

Found on the label or the EnergyGuide sticker. Higher is more efficient.

Number of units

How many identical units run.

Hours a day it runs

Hours at full capacity. A unit that cycles on and off counts only the on time.

Enter how many days a year you run the air conditioning.

This is an estimate, not a professional calculation. See the disclaimer and the methodology.

The three things that set the kWh

Size. Central systems are sized in tons. One ton is 12,000 Btu per hour, so a 3-ton system is 36,000 Btu per hour.
Efficiency rating. SEER2 is printed on the unit and on the EnergyGuide label. A higher number means less electricity for the same cooling.
Hours of use. The hours at full capacity per day, times the days you cool.

The formula

Power in kilowatts = capacity in Btu per hour ÷ rating ÷ 1,000. Energy in kWh = power × hours. Cost = kWh × price per kWh.

For a 3-ton system (36,000 Btu per hour) with a rating of 16, the power is 2.25 kW. Running 8 hours a day for 30 days that is 540 kWh. At the U.S. average price of 16.5 cents per kWh (2024), it costs $89 for the 30 days. The size, rating and hours are assumptions for this example.

How size and rating move the monthly kWh

The table shows the kWh for 30 days at 8 hours a day at full capacity, and what that costs at 16.5 cents per kWh. The ratings and hours are assumptions for illustration; replace them with yours in the calculator.

kWh and cost for 30 days at 8 hours a day, by size and SEER2 rating (assumed values)
Size	Rating 14	Rating 16	Rating 18	Rating 20
2 tons	411 kWh, $68	360 kWh, $59	320 kWh, $53	288 kWh, $47
3 tons	617 kWh, $102	540 kWh, $89	480 kWh, $79	432 kWh, $71
4 tons	823 kWh, $136	720 kWh, $119	640 kWh, $105	576 kWh, $95
5 tons	1,029 kWh, $170	900 kWh, $148	800 kWh, $132	720 kWh, $119

Hours matter as much as the rating

Raise the same 3-ton, rating 16 system from 8 to 12 hours a day and 30 days use 810 kWh instead of 540, costing $133. A hot spell, a poorly insulated house or a thermostat set low all add hours. A better rating reduces the kWh for each hour, but cannot make up for a house that needs the system to run all day.

Check against your own bill

Compare a summer month with a mild month on your bill. The difference is roughly what cooling adds. If the calculator gives a very different number, adjust the hours until it matches, and you will have a better estimate for next summer.

The calculator uses one flat price and ignores fixed charges, taxes and demand charges. See the monthly electric bill calculator for a full bill.

Frequently asked questions

How many kWh does a 3-ton central AC use?

It depends on the rating and the hours. The power is 36,000 divided by the rating, in watts. At a rating of 16 that is 2.25 kW, so 8 hours at full capacity is 18 kWh. Use the calculator for your own numbers.

What is SEER2?

It is the seasonal efficiency rating of a central air conditioner, which replaced SEER under the current test procedure. A higher number means less electricity for the same cooling.

Why does my bill go up more than the calculator says?

Your hours may be longer than you think, the rating may fall in extreme heat, or other loads may rise with the weather. Taxes, fixed charges and tiered prices also change the bill.

Does running the fan only use much power?

The calculator does not cover it. The fan of the indoor unit draws power too, and the rating already includes the electricity of the system when it cools.