Air Conditioner Room Size Calculator (BTU to Room Size Chart)

This AC Room Size Calculator answers your questions about how many BTU to cool a room of various sizes, so you’ll choose the right AC unit for the job. It is ideal for window and portable air conditioners.

There’s also a handy AC Unit Size for Room Size Table that answers questions like – How big a room will 12000 BTU cool?

Pick HVAC Air Conditioner Room Size Calculator

This calculator is simple to use, and it immediately shows you the square foot per BTU – which comes to about 1 square foot per 20 BTU.

Air Conditioner Room Size Calculator

What is the 8000 BTU air conditioner room size? Type 8000 into the calculator, and the answer is 400 square feet. (Example 1)

What is the 5000 BTU air conditioner room size? Use the calculator to determine that a 5000 BTU window AC will cool a room up to 250 square feet. (Example 2)

How large is your air conditioner? The number of BTU of a window or portable AC unit should be found on the metal tag located on the side or back. It’s listed in the Owner’s Manual too.

The Table below allows you to go from room size to BTU needed – or if you know the number of BTU, you can see how large a space it will cool.

If you want to know how to calculate BTU for a room, you can use the calculator for trial and error – sort of use the calculator “backwards.”

Plug in different common AC sizes like 6000, 8000, 12000, 18000, etc., until you find one that fits the size of your room within 50 square feet or so.

AC Size Room Size Table

As a general rule, about 20 BTUs of cooling are required per square foot of space. That means a 12000 btu air conditioner room size is 600 square feet.

Other examples follow.

How Many Square Feet Will A 5,000 – 24,000 Btu AC Cool

Cooling Capacity (BTU):Room Size:Examples:
2,000 BTU50 sq. ft.tiny room, tent
5,000 BTU100 - 150 sq. ft.10x10 room, 12x10 room, 12x12 room 
6,000 BTU150 - 250 sq. ft.12x20 room
7,000 BTU250 - 300 sq. ft.16x16 room, 12x24 room
8,000 BTU300 - 350 sq. ft.18x18 room, studio apartment
9,000 BTU350 - 400 sq. ft.18x20 room, studio apartment
10,000 BTU400 - 450 sq. ft.20x20 room, 1-bedroom apartment
12,000 BTU450 - 550 sq. ft.22x22 room, 22x24 room
13,000 BTU550 - 650 sq. ft.25x25 room, apartment w/ open floor plan
14,000 BTU650 - 700 sq. ft.2 rooms, small apartment
15,000 BTU700 - 800 sq. ft.25x30 room, larger apartment
18,000 BTU800 - 1,000 sq. ft.30x30 room, small home, 3-bdrm apartment
22,000 BTU1,000 - 1,200 sq. ft.small home, 3-4 bdrm apartment
24,000 BTU1,400 - 1,500 sq. ft.medium home, 4-bdrm apartment
30,000 BTU1500 - 1700 sq. ft.medium home, 4-bdrm apartment

Now, let’s discuss how this table will help you choose the right size air conditioner for the room or zone you want it to serve.

Example 1: Search the Cooling Capacity (BTU) column for the AC size you have.

For example, let’s say you have a 14,000 BTU AC. Find 14000 in the left column, and look at the middle column, the Room Size column, to see it will cool 650-700 square feet.

Is it a portable AC? There’s a little bad news. Unfortunately, the actual cooling capacity of portable ACs is a little more than half of what is listed in the old rating system. For example, most 14,000 BTU portable ACs, using the old rating, are rated at about 7,700 BTU by the new rating.

See Portable AC BTU DOE vs BTU Ashrae for the reason why. Just keep that in mind when you’re trying to cool and dehumidify your room or home using a portable air conditioner.

Example 2: If you haven’t bought an AC unit, use the middle Room Size column.

For example, find the number of square feet you want to cool, and it shows the right size AC in the left Cooling Capacity (BTU) column.

Example 3: Some readers won’t know how large the room is and don’t have the means to measure it. They ask questions like – I don’t know how many square feet the room is, but it is a normal size living room.

The answer is best found in the right column of Examples. Browse down the column until you find an Example that sounds right. In this case, a 12×20 room or 16×16 room is the best answer.

Of course, knowing the square feet of a room is the right way to get an accurate answer to sizing a room AC.

Additional Examples:

You can see from the AC BTU Room Size table that an 8000 BTU air conditioner is the right size for 300 to 350 square feet. The examples give you an idea of the rooms, such as an 18×18 living room or a very small apartment.

Question: I have a 10,000 BTU AC. What is the 10,000 BTU air conditioner room size?

Answer: Let’s use the Table to find out. Use the left column to locate 10,000 BTU. Move to the right, and the Room Size column shows that a 10,000 BTU AC is the right size for 400-450 square feet.


There is additional information here that might be useful to you.

How do I figure out room square feet?

For a square room, measure the length and the width, and multiply them.

Examples plus how many BTU to cool a room:

A 10L x 10W room is 100 square feet. 5,000 BTU needed.

A 20L x 20W room is 400 square feet. 10,000 BTU needed.

My room is shaped like an L. How do I measure the room?

Divide the room into two rectangles, and do the math for each “leg” of the “L.”

Measure the length times the width for each, and add the totals together.


The long leg of the room is 14 feet wide and 20 feet long.

The short leg of the room is 8 feet wide by 12 feet long.

14 x 20 = 280 square feet

8 x 12 = 96

280 + 96 = 376 square feet

How many square feet will a 10000 BTU AC cool?

Using the AC Cooling Capacity Calculator or the AC Size to Room Size Table, you can see that a 10000 AC will cool up to 500 square feet.

Will a 24,000 BTU AC cool a small apartment?

If you go by square feet only, then yes, it has enough cooling capacity to do the job.

However, if the rooms are closed off from one another – rather than an open floor plan – the cooling won’t reach into the rooms unless you use fans to direct airflow. You might be better off using two smaller window ACs. Of course, a central air conditioner or ductless mini split system might be an option if you own the apartment and have the freedom to install a central HVAC system.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

Leave a Comment Protection Status