BTU Calculator

Choose one of the following:

Home BTU calculator

Enter Square Feet of your entire Home:

0 square feet

How many occupants in your home?:

1 people

Roughly, how old is your house?

Would you describe your climate as:

Do you have a basement?



This calculator should only be used to estimate your building’s BTU needs. You should get a professional BTU estimate done by your local HVAC company to get a better picture of what size unit you need.

Room BTU calculator

Enter Square Feet of Room to be Cooled:

100 to 150 square feet

How is the Room Insulation?

Average people

Is the Room Very Sunny?

Is This Air Conditioner for the Kitchen?



This calculator should only be used to estimate your building’s BTU needs. You should get a professional BTU estimate done by your local HVAC company to get a better picture of what size unit you need.

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.

Need To Buy A New AC Unit OR Heater?

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.

What Our Clients Have to Say

    • Geiger Mechanical is truly a reputable company and certainly number one for service in my book. Shawn, the repair manager was extremely helpful and professional. I would recommend them for both installation of a new system as well as repairs on your existing AC.

      George Maloley - Geiger Mechanical George Maloley
    • We were visiting our Florida home from New York, when on one of the hottest days in August the air conditioning was not working. We called Geiger Mechanical & James Shelton worked to get the air up & running in no time. He was courteous & sympathetic, working hard to repair our central air…we have a warranty & Geiger Mechanical stands behind their work, they are available 24/7… Thank you!

      Karin Reilly - Geiger Mechanical Karin Reilly
    • Service was completed in a timely manner and my technician was extremely knowledgeable. All services were explained to me prior to being completed as far as the need and cost are concerned. My air conditioning unit has been problem-free all year and I believe it’s because of the professional maintenance that I get yearly from Geiger Mechanical.

      John Andres - Geiger Mechanical John Andres