how many btu air conditioner do i need for a room

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

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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:

Air Conditioner 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. Obviously, the problem arises when you have a very small 12×12 room, for example. According to the US Department of Energy directive, the most appropriate size of an air conditioner would be 2,880 BTU unit. The best you can do here is to buy a small 5,000 BTU window or small 8,000 BTU portable AC unit (more about smallest AC units here).

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.

49 thoughts on “How Many BTU Air Conditioner Do You Need? (BTU Calculator)”

  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.

      • I have a 26 by 30 room 10 ft walls plus 3 ft to ceiling sun hits direct it’s 780sqft how many btus is recommended going to install two ceiling fans thanks

        • Hello Carlos, with 10 ft ceiling the two fans is a good idea. The room has quite a volume; you would need about 25,000 BTU devices. 2 12,000 units might do the trick as well.

          • Hello Carlos, the 30,000 BTU mini-split will do the job very well. It’s always better to have a little bit bigger capacity than a little bit too weak a unit. 36,000 BTU would be an overkill.

  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.

  8. Live in Central California Modesto it gets super hot in the Summer I’m in a 23 by 25 master using a 5,000 btu. I’m thinking of getting an 8,000 btu the 5,000 btu just isn’t cutting it. I have three windows one being a huge 12 by 6 and it’s located to the west the whole window gets very hot midday. Should I get the 8,000 btu?

    • Hello Edward, you’re correct, the 5,000 BTU unit is not enough. 23×25 master bedroom is 575 sq ft. Given that you’re in sunny California with 3 windows, even the 8,000 BTU might not be enough. For your situation, a 12,000 BTU or even 14,000 BTU would be recommended.

  9. I have an enclosed patio room, it is 20 by 15′ with large windows on three sides. What size portable uni
    t do I need?

    • Hello Harold, for a 300 sq ft patio you would need 6,000 – 8,000 BTU unit. Portable air conditioner would probably be the most convenient.

  10. Good Morning. I have a office room size of 22ft x 30 ft with ceiling height of 9 ft. No direct sunlight but evening sun rays through two glass window. How much BTU do I need to cool the room? Is there any standard that the temperature of the room should within a particular time and what other specifications do I need for a AC while buying like CMH, Cooling Capacity.

    • Hello Sivaram, a 660 sq ft room with low sun exposure would need, roughly speaking, 14,000 BTU AC unit. The only standard for BTU size is the EPA recommendation of about 20 BTU for every 1 sq ft of a room; other factors may apply as well. In your situation, a 14,000-15,000 BTU should do the job well.

    • Hello Kerwyn, we have to do a bit of sq m to sq ft conversion here. 100 m2 living room is equal to 1076 sq ft. With +4,000 BTU for the kitchen, you’re looking at 28,000 BTU device. 30,000 BTU to be safe.

    • Hello James, the usually 15,000+ BTU mini split units need run on 220V. If you’re looking at a 12,000 BTU 220V model, there is a chance the same mini split is available with 115V and double the amperage. The key here might be the heater. If it’s a 18,000 BTU heater, for example, the whole unit will usually need 220V.

  11. I have a Sunroom that’s 17 Ft. by 17 Ft. with a ceiling height 8 1/2 Ft.
    3 of walls are all glass top to bottom. ( room built 1963 ) It also has a very heavy Sun exposure. Located above this added on room is an open attic… can you help

    • Hello Hugh, that’s one hell of a room. Standard 300 sq ft room, for example, would need at least 6.000 BTU device. With the added 1/2 ft of the ceiling and the 3 windows, you should probably check out 10,000 BTU units.

  12. Hi,
    I’m looking to use a portable air conditioner in my garage. Its 683 sq ft with an 11 ft ceiling. I live in central North Carolina. Direct sunlight on insulated garage doors during the afternoon. Garage walls are foam insulated. Four windows, three of which get direct sunlight. Windows are doubled pane. Cement floor. According to your BTU calculator I would need 18,837.5 BTUs. Not sure if they make that size AC in a portable? So, would two 10,000 BTUs work or 14,000 BTUs work just as well?

    • Hello Daryl, the biggest residential portable AC units have a maximum cooling capacity of 15,000 BTU. It’s an electrical thing; if you want 15,000 BTU+, you would need 220V instead of 115V, or alternatively, you would have to double the Amps, which is not ideal. In your situation, you would probably need two units, yes. 2 x 10,000 BTU would make sense. Maybe a combination of 14,000 BTU and 8,000 BTU would be smarter; you only run 14,000 BTU most of the time but during a really sunny day, you also turn on the 8,000 BTU unit.

  13. Hi, I’d like to change window AC unit to a new one. The old one I’m using is 5,200 BTU and it’s not cold enough for summer and now it fails to work properly. My room size (long shape / Studio with kitchen) is 32×11 ft. ( 350 sq.ft.) with 8 ft ceiling, highly sun exposure side of the building (3 windows size: 3×5.2 ft ). I have 2 choices of AC 8,000 BTU or 13,000 BTU. ( someone has extra AC and offer 1 from these 2 to me).

    Which ones should I use? Consider from my information.

    I’ve checked online, it recommended 8,000 btu but with my room size & conditions(very sunny), some website said I should consider to add more BTU than a regular BTU calculation. I’m aware if I use 13,000 BTU, It probably cold more than enough but I concern about electricity bill.

    Normally, I use 20″ portable fan to help the air circulation for AC as well.

    Thankyou so much.

    • Hello Pond, your dilemma is understandable. An average 350 sq ft room would need a 7,000 BTU unit. However, the 3 big windows can really increase the size of the air conditioner you need.

      Of the two choices, 8,000 BTU would be the optimum one. It’s a big increase from 5,200 BTU and it will probably be much more cost-effective than 13,000 BTU device. The rule of thumb is to buy an AC unit that’s a bit bigger than what you actually calculate; in your case, that would be something like a 10,000 BTU device. However, if the choice falls between 8,000 BTU and 13,000 BTU, an optimistic view is that 8,000 BTU should do the job well without increasing the electricity bill significantly.

      • Thankyou very much for your suggestions and ideas. The 8000 BTU will be my final choice.

        I am also thinking to add window films like reflective one to help cut down the sunlight and the heat.

        Thankyou so much again!

  14. Hi
    I am living in the Caribbean, my entire house is 30 * 20 ft, one bed room is 11 * 9 ft floor to ceiling throughout the building is 9 ft. The house is elevated and has wooden floors now can you advise say if i should buy the 4000 BTU for my room or splurge and buy the 12,000/14,000 BTU for the entire house?


  15. I have a lanai 200 square feet with aluminum enclosure and acrylic windows. What size portable AC would work? In the summer here central Florida the room fells like an oven!

  16. Hi, I’m looking to replace a window air conditioner for a 240 sq ft living room with 8 ft ceiling and average sun in Connecticut. The room has a 48 in open doorway to a 90 sq foyer (directly opposite the window with the AC unit) and a 30 open doorway to a 200 sq ft dining room (to the side). The current 8,000 BTU unit does not cool the living room sufficiently. Could I go with a 10,000 or 12,000 BTU unit? Or do I need to get another unit for the dining room (which I’d prefer not to do, as I’m mainly looking to cool the living room)? Thanks for the advice!

    • Hello David, in most cases 8,000 BTU should be more than enough for a 240 sq ft room. However, in your situation with a big window area, the 8,000 BTU unit might struggle to achieve the required temperature. It’s better to be safe than sorry; given the high overall window area, the 12,000 BTU device would be a safer choice.

  17. It is so kind of you to field these questions.

    Here are the specs of my apartment:
    Ceilings: 8.5′
    Central hall area: 8′ x 5′
    Rooms off each side of the hallway:
    Living room: 13′ x 15′ (very warm—southern exposure, over the building boiler room)
    Kitchen: 9′ x 13′ (northern exposure, but warm because of the gas stove)
    Bedroom: 12′ x 12′ (northern exposure)
    Bathroom: 8′ x 8′ (northern exposure, I don’t bother to cool it)

    Up to now I’ve had window units in both the living room and the bedroom. A friend is suggesting that it’s possible to cool this kind of layout with only one window unit (which room?) & good fans strategically placed. I have my doubts. What do you think?

    Thank you!

    P.S. I live in southwestern Connecticut. Humidity is high and in recent summers the temperatures are sweltering for 6-8 weeks.

    • Hello Meg, the total area to cool down is 560 sq ft. According to the EPA, you would have to multiply that number with 20 to correctly size your air conditioner unit. Of course, other factors such as sun exposure and your location can significantly increase the size of the AC unit that would be most appropriate.

      Your friend is right. A 15,000 BTU or 18,000 BTU device could theoretically cool down the entire apartment. The fans are also useful in order to distribute the cooled air throughout the apartment. What size are the 2 window units that are currently installed?

      • Hello again,

        The living room unit is 6,500 BTU and the bedroom unit is 6,000 BTU. I use them only for those rooms. The BTUs are more than adequate for the spaces, but the units are too old to work properly and need to be replaced.

        The configuration problem I anticipate with using a single unit for the whole apartment is that the air flow from bedroom to living room involves passing through a narrow doorway and make a dog-leg turn. I look on fans as efficiency boosters, not as mandatory links in the cooling chain, if you see what I mean. Nor do I want to end up blasting the AC in one room but still getting an inferior result in the other.

        Cooling the living room and the kitchen as one consolidated space is a much easier proposition. Until this summer, I haven’t minded having a hot kitchen. But with the need to work from home now, it would be a huge benefit to have another fully habitable room.

        I’m investigating the Midea U Inverter window units because the position of the compressor should make for quieter functioning. They get excellent reviews, and the sturdiness of the mounting looks like it might save wear and tear on the units, given that I must install and uninstall them every year. Amazon has them in 8,000/10,000/12,000 BTU models.

        Here’s what I’m thinking now. Get two air conditioners. A less powerful one just for the bedroom, a more powerful one to handle the two hottest rooms (living room and kitchen) together.

        I need to keep an eye on the finances, but this is an infrastructure upgrade. 🙂 I’d like to get it right the first time and not have to think about the AC for another ten years!

        Thanks again for helping me to think this through!

        • Thank you for the insight; I’m sure it will be most helpful for everybody who is experiencing similar problems. In short, the logic you’re using is very sound, you know exactly what you’re talking about. Have a cool summer!


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