How Much Does Central Air Conditioning Cost to Run?
Updated April 17, 2026
Just want the number? Use the energy cost calculator.
A typical 3 ton central air conditioner pulls roughly 3,000 to 3,500 watts while it is running, which costs about 50 to 60 cents per hour at the U.S. average electricity rate. Run it the way most homes do in the heat of summer and that lands somewhere around 90 to 180 dollars a month. The spread is wide because three things move the number: the size of the unit, how efficient it is, and how many hours it actually runs.
Here is how those pieces fit together.
The watts to kWh to dollars math
Electricity is billed by the kilowatt-hour, so the cost comes down to three steps.
- Wattage to kilowatts. A 3 ton AC drawing 3,500 watts is 3.5 kilowatts.
- Kilowatts to kWh. Run that unit for one hour and it uses 3.5 kWh.
- kWh to dollars. The U.S. average residential rate is about 17 cents per kWh, according to the U.S. Energy Information Administration.
So 3.5 kWh times 17 cents is about 60 cents per hour at the top of the range, and a more efficient 3,000 watt unit comes in closer to 51 cents. That hourly figure is the number everything else builds on: multiply it by the hours the compressor runs.
How tonnage drives the bill
Air conditioners are sized in tons, where one ton equals 12,000 BTU per hour of cooling. More tons means more cooling and more power draw.
- A 2 ton unit draws roughly 2,000 to 2,400 watts.
- A 3 ton unit draws roughly 3,000 to 3,500 watts.
- A 4 ton unit draws roughly 4,000 to 4,800 watts.
This is also why an oversized AC is expensive to own. A unit that is too big for the house cools the air fast, shuts off, and starts again a few minutes later. That short cycling wastes power and never runs long enough to pull humidity out. If you are not sure your system is matched to your house, the AC and mini-split sizing calculator shows the tonnage your square footage and climate actually call for.
How SEER2 efficiency changes the cost
Two 3 ton units can use noticeably different amounts of power. The difference is the efficiency rating, now measured as SEER2 (Seasonal Energy Efficiency Ratio 2). A higher SEER2 means more cooling per watt.
A new unit sold today has a minimum SEER2 in the 13.4 to 14.3 range depending on region, while high-efficiency models reach the low 20s. The U.S. Department of Energy publishes the current efficiency standards for central air conditioners. Replacing an old SEER 10 system with a SEER2 16 one can cut the cooling portion of your bill by a third or more, because the newer unit delivers the same comfort on fewer watts.
Runtime is the part you control
Wattage and efficiency are fixed once the unit is installed. Runtime is not.
- A mild day where the AC cycles a few hours: a couple of dollars.
- A hot day with the compressor running 8 hours: around 4 to 5 dollars.
- A heat wave with near-constant running, 12 hours or more: 6 to 8 dollars a day.
Stretch the 8 hour day across a month and you get the 90 to 180 dollar range from the top of this guide, with the low end being an efficient unit in moderate heat and the high end an older unit during a hot stretch. A few habits trim the hours: a thermostat set a degree or two higher, shaded windows during the afternoon, and a clean filter so the system is not fighting restricted airflow.
A rough monthly range to expect
For a typical 3 ton system at the average rate, plan on something like this in peak summer:
- Light cooling, efficient unit: around 90 dollars a month.
- Steady daily use: around 130 dollars a month.
- Heavy use, older unit, high local rate: 180 dollars a month or more.
If your local rate is higher than the national average, scale every figure up. At 30 cents per kWh, that 60 cent hour becomes more than a dollar, and the monthly numbers nearly double.
Find your own number
To price your own system you need three things: the unit’s wattage or tonnage, the hours it runs on a hot day, and your electricity rate from a recent bill. Run those through the energy cost calculator and it returns the cost per hour, per day, and per month so you can see what a hotter month or a higher rate does to the total. If you are not sure the unit is the right size for your home, what size air conditioner do I need covers the tonnage math and explains why an oversized system often costs more than a right-sized one.