how many btu air conditioner do i need for a room

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

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.

2 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.


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