how many btu air conditioner do i need for a room

How Many BTU Air Conditioner Do You Need? [BTU Calculator + Chart]

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There are a number of metrics you should know before buying an air conditioner. You have different EER and SEER ratings, power, amperage, voltage, and so on.

The most important metric is the BTU value. It denotes the size of your air conditioner. The bigger the BTU, the more cooling effect an AC unit can provide.

How many BTU air conditioner do you need for your room? There are only 2 rules:

The BTU needed to cool down a room of known footage that can be calculated. According to The U.S. Department Of Energy recommendation for the size of room air conditioners, “…an air conditioner generally needs 20 BTU for each square foot of living space.”

Based on room size, ceiling height and other conditions you can calculate how many BTU air conditioner you need:

BTU Calculator

Calculated BTU:

0.00 BTU

As you can see, the sq ft to BTU converter neatly gives you an idea of what size of air conditioners you should be looking at in an ‘sq ft to BTU’ kind of way.

measuring rooms for air conditioner btu size
Roughly measure the places in which you want to enjoy the cool air thanks to your new AC unit.

If you want to properly cool down a 300 square foot area (or room), you need a 6,000 BTU air conditioner.

The trendy portable air conditioners, for example, have a cooling capacity of 6,000 BTU to 14,000 BTU. According to Go Downsize, the average size of studio apartments in the US is about 500 sq ft. That means that for a small apartment, you don’t need an expensive central air conditioning. You can just install an average-sized 10,000 BTU portable air conditioner which will save you tons of money.

Pro tip: Always buy a little bigger AC unit than this recommendation. Example: When you use the BTU calculator below and get let’s say 10,000 BTU for a 500 sq ft area, start looking for 12,000 BTU air conditioner. Your electricity bill will be a little higher but you won’t need to sweat if you bought an AC unit that’s too small.

To better illustrate what size or an air conditioner you need, let’s have a look at a BTU chart:

Air Conditioner BTU Chart

Room/Area Size:Examples:Recommended BTU:
100-200 sq ft10x10 room, 12x12 room, 14x14 room4,000
200-300 sq ft16x16 room, tiny apartment6,000
300-400 sq ft18x18 room, 20x20 room8,000
400-500 sq ft22x22 room, small studio apartment10,000
500-600 sq ft24x24 room, average studio apartment12,000
600-700 sq ft2 rooms, small apartment14,000
700-800 sq ft2 rooms, average apartment16,000
800-900 sq ft3 rooms, above average apartment18,000
900-1,000 sq ft3 rooms, larger apartment20,000
1,000-1,200 sq ft4 rooms, large apartment24,000

Again, when narrowing down your choice of an air conditioner, knowing how big an area you need to cool is your best friend. Based on that, you can calculate sq ft to BTU and immediately know in what range of BTU values your perfect AC unit should be.

If, for example, you buy a 14,000 BTU portable air conditioner to cool down a 12×12 room, you will have chill cold room and more than $100/year unnecessary cost on your electricity bill.

Perfect BTU Air Conditioner For Room Sizes

The ballpark figure, as recommended by The U.S. Department of Energy, is 20 BTU per sq ft. That is a very good estimate already.

However, to get a perfectly-sized air conditioner with just right enough of cooling power and no energy overspending, you should take into account some additional factors. These are:

  1. Room height.
  2. Local climate.
  3. Sun exposure.
  4. The number and size of the windows.

The BTU calculator and chart work best for standard room height. Obviously, if you have a tall ceiling (older building have +10 ft ceilings), you have to add a bit of cooling power in terms of BTU.

There is also a difference if you live in Texas or in New York. The local climate in Texas in, on average, hotter and therefore you should need an air conditioner with a few 1,000 BTU more.

The same goes for sun exposure. If the room or area you’re looking to cool down is generally facing the sun, you will need a bigger air conditioner.

Additionally, the walls do block the sun very effectively. Windows don’t. If you have big windows and many of them, the sun will heat your house more.

In summary, when do you need an air conditioner with higher BTU than standardly recommended:

  1. If you have high walls.
  2. If you live in a hot climate. Examples: California, Texas, Florida, New Mexico and so on.
  3. If the particular room you want to cool down is facing the sun more often than not.
  4. If you have above-average size and number of windows.

Example: If you have a 500 sq ft sun cabin near Texas with many glass windows, you’re should be looking at 10,000 BTU air conditioners (as recommended). You should be looking at a 14,000 BTU portable air conditioners, for example.

What Does BTU Mean In Air Conditioners (Summary)

BTU in air conditioners is simple a metric of how much cooling effect that particular AC unit can produce.

We want an air conditioner that has just the right amount of cooling effect. That’s why by knowing the square footage of the area we want to cool down, we can calculate how many BTU should our air conditioner have.

The equation for ‘sq ft to BTU’ is quite simple – just multiply the sq ft with 20. That means that a 500 sq ft room needs a 10,000 BTU air conditioner. Do make sure, of course, to buy an AC unit that is a bit stronger if you have high ceilings, live in a hot climate and have an above-average sun in those rooms.

Hope this helps. If you have any questions about your particular room or area you’re buying an air conditioner for (and don’t know how many BTU one you should take), you can ask in the comments and we’ll try to give you an answer as soon as possible.

16 thoughts on “How Many BTU Air Conditioner Do You Need? [BTU Calculator + Chart]”

  1. I have a 15 ft by 15th room with a 9ft ceiling. This room has a door way that goes into another 12 by 13 room.the door way is average size. What btu would you recommend.thank you for your time.

    • Hello David, 15×15 and 12×13 rooms have a combined area of 381 sq ft. Given the additional doorway and above-average ceiling height, you’re looking at a 9,000 BTU unit. 10,000 BTU with an above-average airflow (above 250 CFM) would be a safe bet. Hope this helps.

  2. I am researching the most efficient portable room air conditioner for a 2nd floor, sunny bedroom. The 13’2” by 14’5” bedroom room has cathedral ceilings, a SW facing window that measures 48” by 56” and one occupant. Due to HOA restrictions and a sliding glass window, I plan to get a portable air conditioner. I’ve read about dual hose conditioners and not sure if that’s the best way to go. I’m not sure how to calculate the necessary BTU’s needed. Can you help with any thoughts on this? Thank you, Sue Harig

    • Hello Sue, the 13’2” by 14’5” room has about 190 sq ft. Let’s assume that the cathedral ceiling has a height of 13 ft. Such a bedroom has the same volume as a 310 sq ft room with an 8 ft ceiling height. That would, roughly speaking, require a 6.200 BTU portable AC unit. With that big sliding glass window and a lot of sun, the safe estimate for the most optimum AC unit would be 7.000-8.000 BTU.

      The dual hose portable air conditioners have two key advantages: superb energy-efficiency and they don’t lower the pressure inside the room while running. However, they tend to be bigger – 14.000 BTU or so. If you can find a 8.000 BTU dual-hose one, that would be a very optimum choice. Hope this helps.

  3. Hi David , I have a 25×17’ room with 8’ ceilings in all
    Adjacent hallway with 30 “ doorway hallway is 9×5
    Then doorway into lr and dr 30×21
    There is a wall between lr and dr with a 6 ‘ doorway
    How many btu would I need

    • Hello Peggy, for a 25×17 room (425 sq ft), you would need a 8.500 BTU portable AC. If you add 9×5 hallway (45 sq ft) and LR + DR 30×21 (630 sq ft), the total calculated area is 1.100 sq ft. Roughly speaking, you would need 22.000 BTU cooling power. Portable AC units will hardly handle it, window units or mini split units could do that job well.

  4. Thank you for the useful advice. My small apartment has openings in the wall for AC in the living room and the bedroom, thus I am debating whether to get one 14,000 BTU AC or two smaller ones. Any advice on the subject is appreciated.

    • Hello there, if you need 14,000 BTU AC, one window unit or one mini-split unit would be the best choice. AC units above 15,000 BTU usually need an electric upgrade; which you won’t need here. On the other hand, you can invest in two portable AC units, each of 7,000-8,000 BTU, but those can take some space and need to be vented out of the window. The most elegant solution would be a 14,000 BTU mini-split unit.

  5. Hi there. Question… I’m living in a one bedroom apt in NYC. The AC unit will be for our living room. The living room itself is about 20’7″ x 12.1″. However, it has large windows and on the other side of the living room, there is a kitchen (that doesn’t have any AC). Your advice would be much appreciated!

    • Hello Grace, for the (roughly speaking) 350 sq ft living room you would need a 7,000-8,000 BTU AC unit. However, the kitchen is additional space and for kitchen you usually have to add 4,000 BTU. All in all, 12,000-14,000 BTU would make sense in this situation. You can opt for portable or window AC unit; mini-split unit would be a bit too much.

    • Hello Jackie, 16 x 14 room is 224 sq ft. If we assume a 9 ft high ceiling, average climate and average sun exposure, you’re looking at 5,000-6,000 BTU units. For this size, a smaller portable air conditioner would be most appropriate. You can find some of the best portable AC units here.

  6. I have a 16×16 bedroom on the second floor with 8′ ceilings. My current wall unit is 15 years old and has ALWAYS made the room feel damp. I was told the unit is too big for our size room. I went to local store to size one more appropriately and was told the Frigidaire FFRE153ZA1 15,000 BTU’s is the right one. Of everything I read online, it seems to me that this is too big? Am I correct? What size wall unit would best suit my needs and what Frigidaire wall mounted model am I looking for?

    • Hello Michael, 16×16 bedroom has a total area of 256 sq ft. That means a 5,000-6,000 BTU would be enough. You are right; the 15,000 BTU unit is definitely an overkill for a single room. Conservative choice would be the old Frigidaire FFRA051WAE 5,000 BTU. However, given that you have problems with high humidity, a stronger Frigidaire FFRE0833U1 8,000 BTU makes sense (it comes with 1.7 pints per hour dehumidification; it can draw more than 40 pints of water per day). Hope this helps.

  7. I live in New York. My small apartment is 600 square feet but is broken up into 2 bedrooms, 1 living room, 1 kitchen, 1 hallway, bathroom. I have lots off walls and ceiling is just under 9 feet high. I want to buy a mini split ac system. Would an 18000 BTU unit split into 9000/9000 work? 1 in the front bedroom, 1 in the back bedroom…and leave doors open during the day?

    • Hello Andrew, several rooms, hallways, and kitchen do add to the overall BTU cooling power. You’re right; you would need at least 15,000 BTU device – a 18,000 BTU would be perfect. Two-zone 9000/9000 mini split would be the perfect solution here. You do have to have the door open in order to ensure smooth air circulation. It seems that you already have exactly the right idea what to do.


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