How Much Does It Cost to Run an Air Conditioner? (Window and Central AC)

To find the cost to run an air conditioner, multiply its watts by the hours it runs, divide by 1,000 to get kWh, then multiply by your electricity rate. Utility and university appliance charts list window units at roughly 500 to 2,666 watts depending on size, and central air conditioners at about 2,500 to 7,500 watts depending on tonnage. At the US average residential rate of 18.16¢ per kWh, that formula gives you a reliable estimate for your own unit.

The formula: watts × hours ÷ 1,000 × rate

The Department of Energy's Energy Saver program gives the standard method for estimating any appliance's energy use (DOE Energy Saver):

1. kWh per day = wattage × hours used per day ÷ 1,000
2. kWh per period = kWh per day × number of days
3. Cost = kWh × your price per kWh

DOE notes that the wattage on an appliance's nameplate is the maximum power it draws. If only amps are listed, multiply amps by volts. Most household appliances run on 120 volts, while the largest room AC units and central systems use 240-volt circuits (DOE, DOE: Room Air Conditioners).

How many watts does an air conditioner use?

Wattage depends on size and efficiency, so check your unit's label first. If you don't have it, these published charts give typical values.

Window and room air conditioners

An appliance usage chart from Jackson Energy lists these average wattages by cooling capacity (Jackson Energy appliance chart):

Window/room AC size	Average watts
6,000 Btu/h	750
10,000 Btu/h	1,200
12,000 Btu/h	1,600
14,000 Btu/h	1,875
16,000 Btu/h	2,125
18,000 Btu/h	2,395
20,000 Btu/h	2,666

A household electrical usage chart from Indiana University of Pennsylvania's facilities office lists small, medium and large window units at 500, 900 and 1,440 watts (IUP Facilities chart). Newer, more efficient units can draw less than older ones of the same capacity.

Central air conditioners

The Jackson Energy chart lists central systems by size (Jackson Energy):

Central AC size	Average watts
1.5 ton	2,500
2 ton	3,200
2.5 ton	3,500
3 ton	4,500
4 ton	6,000
5 ton	7,500

The IUP chart also lists a 2.5-ton central AC at 3,500 watts and running the central system's fan only (no cooling) at 352 to 425 watts (IUP). Both charts describe their figures as approximate averages.

Use your unit's efficiency rating

DOE explains that a room AC's Energy Efficiency Ratio (EER) is its cooling capacity in Btu per hour divided by its power input in watts (DOE). Rearranged, watts ≈ Btu/h ÷ EER. If your label shows the capacity and EER, you can estimate the running wattage directly.

Worked examples

These examples use wattages from the charts above. The hours are assumptions for illustration; your AC's actual run time depends on weather, insulation and thermostat setting. Costs are shown at an example rate of 15¢ per kWh. To use the current national average, multiply the kWh column by 18.16¢.

Unit (chart wattage)	Assumed hours/day	kWh per day	kWh per 30 days	Cost per 30 days at 15¢
Small window unit (500 W)	8	4.0	120	$18.00
Medium window unit (900 W)	8	7.2	216	$32.40
12,000 Btu/h room unit (1,600 W)	8	12.8	384	$57.60
2.5-ton central AC (3,500 W)	8	28.0	840	$126.00
4-ton central AC (6,000 W)	8	48.0	1,440	$216.00

Example math for the 2.5-ton system: 3,500 W × 8 hours ÷ 1,000 = 28 kWh per day; 28 × 30 = 840 kWh; 840 × $0.15 = $126.

Why your real cost may differ

• Compressors cycle. An AC that is "on" all day doesn't run its compressor every minute. Count the hours the compressor actually runs, which is lower in mild weather and higher in a heat wave.
• Nameplate is a maximum. DOE notes nameplate wattage is the maximum draw, and actual use depends on the setting (DOE).
• Rates differ. EIA notes electricity prices are usually highest in summer, when total demand is high (EIA), and some utilities charge more during afternoon and early-evening peak hours.
• Measuring helps. DOE says plug-in usage monitors ($25 to $50) work on 120-volt devices, but not on 240-volt equipment such as central air conditioners (DOE). For central AC, your utility's hourly smart meter data is often the best guide.

Cost per hour of AC run time

To find the cost per hour, divide the wattage by 1,000 to get kWh per hour of compressor run time, then multiply by your rate. Using the chart wattages above:

• 500 W small window unit: 0.5 kWh per hour
• 1,200 W 10,000 Btu/h unit: 1.2 kWh per hour
• 3,500 W 2.5-ton central AC: 3.5 kWh per hour
• 7,500 W 5-ton central AC: 7.5 kWh per hour

Multiply any of those figures by 18.16¢ to see the hourly cost at the current national average residential price, or by the rate on your bill for a local figure.

Room AC vs. central AC

DOE notes that room air conditioners are less expensive to operate than central units, because they cool only the space you are using. Room units generally range from 5,500 to 14,000 Btu per hour, and DOE's rule of thumb is about 20 Btu for each square foot of living space (DOE). If you mainly need to cool one or two rooms, a properly sized room unit can use far fewer kWh than running a whole-house system.

How much of your bill goes to air conditioning?

EIA reports that air conditioning was the largest single use of residential electricity in 2020, at 19%, and that 89% of U.S. homes used air conditioning that year. Homes in the South tend to use more air conditioning (EIA: Electricity use in homes). EIA's summer bill outlooks identify weather as the biggest source of uncertainty, with hotter-than-expected temperatures able to push bills higher (EIA Today in Energy).

Choose the right size room AC

An oversized unit costs more and doesn't cool better. ENERGY STAR warns that oversized units can cool a room before removing humidity, leaving it damp, and DOE says a properly sized unit that runs longer is more efficient (ENERGY STAR, DOE). ENERGY STAR's sizing guide (for 8-foot ceilings) includes:

Area to cool (sq ft)	Capacity needed (Btu/h)
150–250	6,000
300–350	8,000
400–450	10,000
450–550	12,000
550–700	14,000
700–1,000	18,000

ENERGY STAR suggests reducing capacity 10% for heavily shaded rooms, increasing 10% for very sunny rooms, adding 600 Btu/h per person beyond two regular occupants and adding 4,000 Btu/h for a kitchen (ENERGY STAR).

How to lower the cost of running your AC

1. Raise the setpoint. ENERGY STAR suggests about 78°F for room ACs, and DOE recommends setting the thermostat as high as is comfortable (ENERGY STAR, DOE).
2. Set it back when you're away. DOE says a 7°F to 10°F setback for 8 hours a day can save as much as 10% a year on heating and cooling (DOE).
3. Add a ceiling fan. DOE says a ceiling fan lets you raise the thermostat by about 4°F without reducing comfort (DOE).
4. Keep heat away from the thermostat. Lamps and TVs near a room AC's sensor make it run longer (DOE).
5. Install it properly. ENERGY STAR says a poorly installed unit can leak air like "a 6-square-inch hole" and recommends leveling the unit so it drains correctly (ENERGY STAR).
6. Seal and insulate. The EPA estimates an average 15% savings on heating and cooling from air sealing and insulation (ENERGY STAR).

Next steps

Enter your unit's wattage and daily hours in our appliance energy cost calculator, and check your local rate on the electricity rates by state page, since your cost per kWh may be well above or below the national average. Compare other appliances on our cost to run pages, or read how to lower your electric bill for more ideas.