Informational Guide

How Many Watts Does a Window AC Use?

We discuss how many watts a small window AC uses. Learn about your air conditioners’ electricity consumption and how you can use them efficiently.

by Ian Haynes

The average household in the US spends more than $2000 on electricity bills every year, and this average will only increase with more usage.

An air conditioning system is arguably one of the best and most effective methods to cool down your house. But do you know how many watts does your window AC use per hour, day or month?

Knowing this will help you save both money and energy by a significant margin. Want to know more? Read on as we discuss how many watts does a small window AC use!

Mini Split System in Living Room
Checking The Specifications For Watts

The first way to do this is to look into the product’s specification sheet. You can locate the power ratings (in watts) and amperage (in amps) in the voltage section (volts).

Checking The Specifications For Amp & Volts

If you don’t find wattages of the unit, look for the volts and ampere ratings in the specification sheet. Multiple volts with amperes, and you’ll have your air conditioner’s watts.

For example: 10 amps x 120 volts = 1200 wattages

Use BTU And EER Rating

The third way is to use the EER and BTU ratings of the unit to calculate how many watts a small window AC consumes. Simply divide BTU ratings by EER ratings of the unit.

For example: 6000 BTU / 10 EER = 600 watts

Senville SENL-09CD Energy Guide

How To Calculate The Number Of Watts Your Window AC Used?

Understanding how many watts your air conditioner consumes helps you save electricity and money.

To calculate watts, all you have to know is the volts and amperes of your device and use the following multiplication formula:

Watts = Amps x volts

Suppose the current is 4 amps, and the volts is 120, put these values in the watts equation, and you’ll have the number of watts used.

Watts = Amps x volts = 4 x 120 = 480 watts

You can also use EER and BTU method to calculate watts. Here’s the equation for that:

Watts = BTU / EER

Moving on, let’s suppose you have an AC unit with 5000BTU capacity and a 10 EER rating. Put these into watts formula.

Watts = BTU / EER = 5000 / 10 = 500 watts

Below is the table to show how much power (in watts) a window AC uses per BTU from 5000 to 18000 BTU.

A general principle to calculate how many watts an AC consumes is to divide the BTU by 10. For instance, a 5000 BTU air conditioner consumes 500 watts of energy.

In the following table, we will assume the EER ratings of all air conditioners are between 8-12. This is how you’ll find a different watts range for the same AC units.

BTU Wattages
5000 417 – 625 Watts
6000 500 – 750 Watts
8000 667 – 1000 Watts
10000 833 – 1250 Watts
12000 1000 – 1500 Watts
15000 1250 – 1875 Watts
18000 1500 – 2250 Watts

What Is The Average Cost Of A Running A Window AC Unit?

On average, your window AC will cost you between $0.07-$0.20 per hour, and if it’s functional for 8 hours straight, the average cost will increase to $0.56 –$1.6.

Meanwhile, the average price per month will be anywhere from $15 to $40.

If you want to calculate the average cost of running a window AC unit, make sure you’re armed with the  following:

  • Number of Wattages the AC Uses
  • Kilo-watts per hour (kWh) the power company charges ($0.13 is the “national average”)
  • How many hours you intend to run your window AC per day

Then, use the simple, universal formula to calculate the cost of running per hour, day, and month:

Wattages x 1 (usage hour) / 1000 x 0.13(kWh) = cost of running (per hour)

Let’s suppose your unit consumes 500 watts; put it into the above equation.

500 x1 / 1000 x 0.13 = $0.065 (per hour)

Assume that you’re using it 8 hours per day, the running cost per day will be:

$0.065 (hourly cost) x 8 hours = $0.52 per day

If you multiply it by 30 days, you’ll get the monthly cost of running an AC unit.

$0.52 x 30 = $15.6 per month 

Other Factors That Affect Electricity Consumption

Though there are many, here are the most significant ones:

Climate/Outdoor Temperature

For an AC unit to operate efficiently and effectively, the discharged air temperature from the unit must be higher than the outside temperature.

If there isn’t a significant difference between the two, your air conditioner will have to operate harder, which automatically increases electricity consumption.

Window AC in Winter
Room Size

One of the most prominent and crucial factors is room size. This is because a bigger room will need more cooling, meaning that it will need to remove a certain amount of heat to provide cooling.

The room size is also affected by other variables such as insulation and the furniture present in the room.

AC Size

If you want to enjoy better and effective indoor cooling with low monthly utility bills, you must choose a proper size air conditioner for your room.

This is important because if you choose a bigger AC size (in BTUs), it will cool down the entire space in less time but cost a lot more money.

On the contrary, smaller-sized window air conditioners will consume lesser electricity but will take longer to cool your room compared to the large-sized AC.

Therefore, always choose the right-size air conditioning system to minimize the electricity cost and maintain consistent cooling.

Thermostat Settings

No matter what the thermostat settings, your air conditioning system will take the same time to cool the space. The only real difference in both conditions will be electricity consumption.

For example, people who run air conditioners at 16°C or 18°C may have to pay lower power bills than those setting the thermostat at 28°C or 30°C.

Seasonal Energy Efficiency Ratio

The Seasonal Energy Efficiency Ratio (SEER) informs you about the watts your air conditioning system will use to generate BTUs.

It will help you measure how effective and efficient your AC unit is and how it will impact your monthly energy bills. Are you wondering how your unit will do this?

AC units with less than 10 SEER ratings consume more power than air conditioners with a standard ten and above SEER ratings.

And air conditioners with more than ten SEER and EER ratings are incredibly efficient units, whereas models with a 14.5 SEER are the most efficient – having an Energy Star certification.

energy-savings list

How To Save Money When Using Window ACs

There are several ways you can save money when using a window air conditioner. Here are the three most feasible ways:

Don’t Confuse The Thermostat

Here’s a fact: although the central air conditioning systems are smart, they don’t have the slightest idea about what causes the heat; they only know the room is hot.

Items such as a TV, lamp, or any other electronic device get warm, and when you have them near your AC unit or thermostat, it will make the unit think your room is hotter than it is. Smart window AC units are popular as they combine heat control and reliability in the home.

Cover Your Air Conditioner

If the air conditioner is subject to direct sunlight, it will not perform as effectively as it would in a shaded place, so make sure to cover it up to remain safe from overheating.

Clean The Filter

Dirty air filters will make it harder for the unit to provide cooling, compelling them to work longer. However, if you clean and replace the filters regularly, not only will you save money, the unit will also last longer.

Cleaning Air Filter

People Also Ask (FAQ)

Do Window Air Conditioners Use A Lot Of Electricity?

Compared to the central air conditioning system, window air conditioners don’t use a lot of electricity – consuming less than one-third in comparison.

What Is The Electrical Requirement To Run A Window AC?

The electrical requirements to run a window AC is 115, 125 and 220 voltage outlet with an amp rating from 15-20. 115 and 125 are ideal for smaller units, whereas air conditioners with 15,000 or higher BTU capacity need a 220 voltage circuit.

Does Higher Wattage Of Window AC Use More Electricity?

Yes, the higher the wattage of window AC, the more electricity is required, making it expensive to run. For instance, a 1000 watt air conditioner spends 1 kWh of power/hour; however, a unit with 1500 wattages consumes 1.5 kilowatt-hours of power/hour.

Are Higher Or Lower Watt AC Units Better?

Neither higher nor lower watt AC units are better. The most important thing to remember is the room size. If you have a bigger room with more cooling load, a bigger watt AC unit is better, but if the room is smaller, choose a lower watt AC.


Though air conditioners provide a better and faster way to cool your room during summers, if you ignore how many watts your AC uses, you’ll continue to pay heavy bills each month. After all, cooling and heating account for about 50% of household expenses.

Ian Haynes

Ian Haynes is an HVAC writer, and researcher. He has worked on hundreds of articles relating to home cooling, heating and air quality with a vast knowledge of the technical aspects of these types of appliances. Outside of his work, Ian likes exploring Brooklyn with his Labrador. Learn more about the AC Lab team here.