Window AC Electricity Cost: Per Hour, Day and Month

Calculate how much a window air conditioner costs to run per hour, day, and month using its wattage, cooling time, and your electricity rate.

APPLIANCE POWER USE

WattBasis Editorial Team

9/6/20267 min read

The 30-Second Answer

An 800-watt window air conditioner costs about $0.16 per effective cooling hour when electricity costs $0.20 per kWh. If it accumulates six effective cooling hours each day, it would use approximately 144 kWh per month and cost about $28.80 over 30 days.

That is a calculated example—not a universal average. Your result depends on the unit’s electrical input, compressor cycling, local electricity rate, thermostat setting, weather and room conditions.

For context, the U.S. Energy Information Administration reported a preliminary national residential average electricity price of 18.34 cents per kWh in June 2026. Prices varied substantially by state, so your own utility rate is always the better number to use.

Example snapshot
800 W × 6 effective hours/day × 30 days = 144 kWh/month
144 kWh × $0.20/kWh = $28.80/month

Window air conditioner cooling a bright modern living room

How Much Does a Window AC Cost to Run?

Three numbers determine most of the result: the unit’s electrical input, its effective cooling time and your electricity rate.

Use this formula:

Monthly cost = (watts ÷ 1,000) × effective cooling hours per day × days used × electricity rate

For an 800-watt window AC used for six effective cooling hours per day:

800 watts ÷ 1,000 = 0.8 kilowatts

0.8 kW × 6 hours = 4.8 kWh per day

4.8 kWh × $0.20 = $0.96 per day

$0.96 × 30 days = $28.80 per month

For context, the preliminary average U.S. residential electricity price was 18.34 cents per kWh in June 2026. Prices vary significantly by state and utility, so always use the rate shown on your own electricity bill.

Do Not Confuse These Three Numbers

BTU/h: cooling capacity

BTU/h measures how much heat the air conditioner can remove from a room. It does not tell you how much electricity the unit consumes.

Watts: electrical power

Watts measure the electrical power the air conditioner draws while operating. This is the number you should enter as electrical input in the calculator.

kWh: electricity used over time

Kilowatt-hours measure the electricity consumed over a period of time. This is the unit normally used by electricity companies to calculate your bill.

An 8,000 BTU air conditioner does not consume 8,000 watts. Always look for input power expressed in watts or W.

Window AC Running Cost Formula

Use this formula to estimate the cost:

Monthly cost = (watts ÷ 1,000) × effective cooling hours per day × days used × electricity rate

Example calculation

For an 800-watt window AC accumulating six effective cooling hours per day:

800 watts ÷ 1,000 = 0.8 kilowatts

0.8 kW × 6 hours = 4.8 kWh per day

4.8 kWh × $0.20 = $0.96 per day

$0.96 × 30 days = $28.80 per month

The calculator above performs these steps automatically using your own numbers.

Find the Right Numbers for Your Estimate

Find the electrical input

Check the unit’s label, EnergyGuide label, manual or manufacturer specifications for electrical input expressed in watts.

If the label only provides volts and amps, multiplying volts by amps can provide a rough estimate. Manufacturer-stated wattage or measured consumption will normally be more accurate.

Estimate effective cooling hours

The number of hours an air conditioner is switched on is not always the number of hours it operates at full cooling power.

A conventional compressor cycles on and off as the room reaches the selected temperature. A variable-speed compressor can reduce its output instead.

For example, an AC may be switched on for eight hours but accumulate only five or six equivalent hours at its rated wattage.

Enter your electricity rate

Find the variable electricity rate on your utility bill. If electricity costs 20 cents per kWh, enter 0.20, not 20.

Fixed monthly fees are normally excluded because they may remain unchanged regardless of how much electricity the AC uses.

Window AC Cost by Cooling Time

The following examples use an 800-watt unit, an electricity rate of $0.20 per kWh and a 30-day month:

2 hours per day: 48 kWh and $9.60 per month
4 hours per day: 96 kWh and $19.20 per month
6 hours per day: 144 kWh and $28.80 per month
8 hours per day: 192 kWh and $38.40 per month
12 hours per day: 288 kWh and $57.60 per month

In this example, every two additional effective cooling hours per day add $9.60 to the monthly cost.

What Makes a Window AC More Expensive to Run?

Two identical air conditioners can produce different electricity costs. The most important factors are:

Outdoor temperature and humidity
Thermostat setting
Direct afternoon sunlight
Room size and ceiling height
Insulation and air leakage
Gaps around the air conditioner
Open doors or windows
Dirty or obstructed filters
Heat from computers, televisions and cooking
Compressor design and cycling
Local electricity prices

The air conditioner is only one part of the system. The weather, room and installation determine how long it needs to operate.

Choose the Right BTU Capacity

Bigger is not always better.

An oversized air conditioner may cool the room quickly but switch off before removing enough humidity. An undersized unit may run for long periods without reaching the selected temperature.

ENERGY STAR recommends using room area as the starting point:

100–150 square feet: approximately 5,000 BTU/h
150–250 square feet: approximately 6,000 BTU/h
250–300 square feet: approximately 7,000 BTU/h
300–350 square feet: approximately 8,000 BTU/h
400–450 square feet: approximately 10,000 BTU/h
450–550 square feet: approximately 12,000 BTU/h
550–700 square feet: approximately 14,000 BTU/h

For a heavily shaded room, reduce the starting capacity by about 10%. For a very sunny room, increase it by about 10%.

Add approximately 600 BTU/h for each regular occupant beyond two. If the unit will cool a kitchen, ENERGY STAR recommends adding 4,000 BTU/h.

Seven Ways to Lower Your Window AC Cost

1. Seal the installation

Check for gaps around the unit and window frame. ENERGY STAR states that a poorly installed room air conditioner can leak as much air as a six-square-inch hole.

2. Clean the filter

Clean the reusable filter according to the manufacturer’s instructions. Restricted airflow can reduce cooling performance and make the unit operate longer.

3. Block direct sunlight

Close blinds or curtains during the hottest hours, particularly on windows receiving strong afternoon sun.

4. Avoid extreme thermostat settings

Selecting a very low temperature does not cool the room instantly. It may simply keep the compressor operating longer.

ENERGY STAR suggests setting the thermostat as high as is comfortable, typically around 78°F.

5. Keep heat away from the thermostat

Do not place lamps, televisions or gaming equipment close to the AC thermostat. Nearby heat can make the unit run longer than necessary.

6. Use timers and energy-saving modes

Use sleep, timer, eco or connected controls to avoid cooling an empty room.

7. Use a fan when it improves comfort

A fan does not reduce the actual room temperature, but air movement may help you remain comfortable with a less demanding thermostat setting.

Is a Variable-Speed Window AC Worth It?

A conventional compressor normally operates at full output and switches off when the desired temperature is reached.

A variable-speed compressor can reduce its output to match the room’s cooling demand. This can improve efficiency, reduce noise and maintain a more stable temperature.

Before replacing a working unit, compare the purchase price, documented energy consumption, expected summer use and your electricity rate.

How to Get the Most Accurate Result

A calculation based on rated wattage provides a useful estimate, but measuring real consumption is more accurate.

Use a compatible plug-in electricity monitor and record several representative days. Measuring only one mild afternoon may not represent consumption during a heat wave.

Run the calculator using three scenarios:

A mild-weather month
A typical summer month
A very hot month

A realistic range is more useful than relying on one number.

Frequently Asked Questions

How much does a window AC cost per hour?

Divide its wattage by 1,000 and multiply the result by your electricity rate. An 800-watt unit at $0.20 per kWh costs approximately $0.16 per effective cooling hour.

How much electricity does a window AC use per month?

An 800-watt unit accumulating six effective cooling hours per day for 30 days would use approximately 144 kWh.

Does it use electricity when the compressor is off?

It may continue using electricity for the fan, display, controls or standby functions. The amount depends on the model and operating mode.

Is BTU the same as wattage?

No. BTU/h describes cooling capacity, while watts describe electrical input power.

Is it cheaper to leave a window AC running all day?

Not necessarily. Cooling an empty room or maintaining an unnecessarily low temperature can increase electricity use.

Can a window AC noticeably increase an electric bill?

Yes, particularly during hot weather or when the unit operates for many effective cooling hours. Use the calculator with your own wattage, rate and cooling time to estimate its contribution.

Calculate Your Own Window AC Cost

Small changes in wattage, cooling time and electricity rate can produce very different monthly totals.

Use the calculator above with the information from your air conditioner and electricity bill. You can also use the WattBasis Electricity Cost Calculator for other household appliances.

WattBasis provides educational energy-cost estimates. Results are not product tests, utility quotes or guaranteed savings.