BTU Calculator

What Size Air Conditioner Do I Need?

Using an air conditioner on a hot day can make the temperatures more bearable, but only if the air conditioner is big enough to cool the area you want it to. On the other hand, purchasing an air conditioner that is too large for the space may mean you’re spending more money, both on the unit and on the energy it requires to run. Get the right-size air conditioner for your needs and make sure you’re comfortable – both physically and financially.

Determining Your BTUs

Air conditioners are sized by the number of BTUs they put out. BTUs stand for British Thermal Units and refer to the amount of energy your air conditioner is using per hour.

To figure out what size air conditioner you require, you first need to determine the amount of BTUs you require. This is done by calculating your square footage.

Break up each room into as many squares and rectangles as you need to be able to measure the entire space accurately. This means separating out closets, bump outs, and hallways each as their own separate area.

Selecting Your Unit

Air conditioners are clearly labeled with the amount of BTUs they need. Consult the following chart to see where your square footage lands in relation to the amount of BTUs. Purchase the unit that best corresponds to the amount of square footage you have.

Square Footage

100 – 150
150 – 250
250 – 300
300 – 350
350 – 400
400 – 450
450 – 500
500 – 700
700 – 1,000
1,000 – 1,200
1,200 – 1,400
1,400 – 1,500
1,500 – 2,000
2,000 – 2,500

BTUs Required


Variations and Variables

While this chart is used as a general rule of thumb for selecting air conditioner size, variations can occur depending on several variables you need to consider.

Shade and Sun

If the room or house you are cooling is heavily shaded, you may need 10 percent fewer BTUs to cool it. If the house or room is very sunny, however, add 10 percent more BTUs.

Room Occupancy

The more people that use the area you are cooling, the higher the BTUs need to be to compete with body heat. As a general rule of thumb, for every person over an initial 2 people, add 600 BTUs.

Hot Appliances

If the room you are planning on installing an air conditioner in is the kitchen, you need to factor in additional BTUs for the stove, oven, and microwave. Add about 4,000 BTUs to the unit size to cover this.

Get a Professional Opinion

If you are unsure about the size of unit you need, or you have trouble calculating the size of area you plan to cool, get a professional opinion. Getting the right-sized air conditioning unit is too important to leave to chance.