How Many BTU Do I Need? (Air Conditioner BTU Calculator)

So you’re preparing to buy an ac unit but don’t what capacity should you get. If you’re a new buyer sometimes companies can fool you by installing an under or oversized ac unit.

Obviously, they’re there to make money so they’ll try to sell big units. But big ac unit consumes large power and their maintenance is also very expensive. So you must get a properly sized ac unit for your home.

Now there are different factors that come into place when buying an ac unit. You need to check your home insulation, you need to consider how hot is your area is, you need to consider how many vents or windows do you have and in which direction they’re located, and etc.

AC BTU Calculator

Note: If you live in a hot area and the sun exposure to your house is very high. Then add 1000 BTUs to the overall btus calculated below. And if you live in a cold region with very little sun exposure (Heavily shaded area) then subtract(minus) the 1000 BTUs to the overall btus below.



Area To Be Cooled (square feet)Capacity Needed (BTUs per hour)
100 to 1505,000
150 to 2506,000
250 to 3007,000
300 to 3508,000
350 to 4009,000
400 to 45010,000
450 to 55012,000
550 to 70014,000
700 to 1,00018,000
1,000 to 1,20021,000
1,200 to 1,40023,000
1,400 to 1,50024,000
1,500 to 2,00030,000
2,000 to 2,50034,000

Why is Choosing the right sized AC so important? 

Choosing the right size ac is very important as it’ll save you from different problems. If you don’t have a right-sized ac unit then you’re house will take more load. And it can cause tripping a breaker. Tripping breaker can also cause parts failure and central ac parts are very expensive. 

How To Select A Proper Size AC Unit?

When it comes to air conditioners it’s important to have a properly sized air conditioner. If you have an air conditioner that’s too large for the room.

Then it’s going to shut off early and not have enough time to dehumidify and remove the moisture leaving you with a very cold environment.

On the other side if the air conditioner is too small for the environment that you’re cooling then the air conditioning will continually run never cooling the room properly never dehumidifying the room properly and also costing you more energy. 

So How do I calculate What Size Air Conditioner I Need?

It’s quite simple you simply measure the square footage of the room 

Square Foot of the room = length of the room multiplied by the width of the room (Length *Width)

If it’s on the main floor you’ll multiply the square footage by twenty. 

If it’s a second floor or a kitchen area multiply that square footage of the room by 35. 

If your ceiling height is over 8 feet I always recommend adding 1,000 BTU for every foot over that 8-foot ceiling height. 

You should also take into consideration the number of people in the room for each person over the first two individuals you must add an additional 600 BTUs. 

For example: 

We’re going to use a room that’s 12 by 17 it happens to be on the second floor with a 9-foot ceiling. 

So first calculate square footage i.e 12*17 =204

Since it’s on the second floor multiply it by 35 i.e 204*35 = 7140 BTUs

We mentioned that the ceiling height was nine-foot so we want to add an additional 1000 BTUs i.e 7140+1000=8140 BTUs.

So this house will need a total of 8140 BTUs approx.

Thing You Should Consider Inspecting Before Installing An AC Unit

The first thing you need to consider is the overall construction of the building in which ac is being installed. You need to take the proper details of the house like material and construction assembly that were used in making your house(i.e. drywall, sheathing, exterior siding materials, structural framing system, roofing materials, etc.  

The next thing you need to consider is the overall orientation of the house. The orientation of the house can greatly affect the sensible heat gain on the house depending on the ratio of windows to opaque walls and the degree of shading from the sun.

Another thing you must consider is ventilation/infiltration. Ventilation and infiltration bring outside air into the conditioned space, impacting the heating and cooling.

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