What size air conditioner do I need?
There are several metrics you should consider before buying an air conditioner. You have different EER and SEER ratings, power, amperage, voltage, and so on.
The most important metric is the cooling capacity (measured in BTU/hr). It denotes the size of your air conditioner.
BTU meaning: British Thermal Unit or BTU/h is a unit that determines the cooling/heating power of an HVAC device (air conditioner, furnace, etc.).
What is BTU is an AC unit? Simply put, it’s the capacity or power of the AC.
The bigger the BTU, the more cooling effect an AC unit can provide.
Here is an example of how you can calculate how many BTUs you need to cool down a 500 sq. ft. area with 8 feet ceilings, average sun exposure, average climate, and not including kitchen (you can find this BTU calculator below and use it for your situation; with 4,000-24,000 BTU room size table):
In short, you would need a 10,000 BTU air conditioner.
How many BTUs do you need to cool down certain square footage of space properly?
There are only 2 rules:
- Not too big. Obviously, you don’t want a 14,000 BTU window air conditioner for a small 12×12 room because it unnecessarily boosts your energy bill.
- Not too small. You don’t want to get hot in the summer because you bought a 6,000 BTU portable air conditioner for a 1,000 sq ft apartment.
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
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.
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 tiny 12×12 room, for example. According to the US Department of Energy directive, an air conditioner’s most appropriate size would be 2,880 BTU unit. The best you can do here is to buy a small 5,000 BTU window or a small 8,000 BTU portable AC unit (more about the 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 expensive central air conditioning. You can 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 a 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 of an air conditioner you need, let’s have a look at a BTU chart:
Air Conditioner BTU Chart; With 12,000 BTU (1 Ton) Room Size Example
Question: What is the 12,000 BTU air conditioner room size? 12,000 BTU is equal to 1 ton; we’re talking about 1 ton AC room size.
Answer: Using the EPA’s 20 BTU per sq ft rule of thumb, the room size of 12,000 BTU air conditioners is 600 sq ft. Equally, 1 ton AC room size is about 600 sq ft.
Here is a table with rough room size estimates for air conditioners with different cooling capacities to help you out:
|Cooling Capacity (BTU):||Room/Area Size:||Examples:|
|4,000 BTU air conditioner room size:||100-200 sq ft||10x10 room, 12x12 room, 14x14 room|
|6,000 BTU air conditioner room size:||200-300 sq ft||16x16 room, tiny apartment|
|8,000 BTU air conditioner room size:||300-400 sq ft||18x18 room, 20x20 room|
|10,000 BTU air conditioner room size:||400-500 sq ft||22x22 room, small studio apartment|
|12,000 BTU air conditioner room size:||500-600 sq ft||24x24 room, average studio apartment|
|14,000 BTU air conditioner room size:||600-700 sq ft||2 rooms, small apartment|
|16,000 BTU air conditioner room size:||700-800 sq ft||2 rooms, average apartment|
|18,000 BTU air conditioner room size:||800-900 sq ft||3 rooms, above average apartment|
|20,000 BTU air conditioner room size:||900-1,000 sq ft||3 rooms, larger apartment|
|24,000 BTU air conditioner room size:||1,000-1,200 sq ft||4 rooms, large apartment|
Example: How many BTU do you need for a 20×20 room? For a 20×20 room, you need about 10,000 BTU of cooling output.
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 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 a chill cold room and more than $100/year unnecessary cost on your electricity bill.
Perfect BTU Air Conditioner For Room Sizes
As recommended by The U.S. Department of Energy, the ballpark figure is 20 BTU per sq ft. That is a very good estimate already.
The simplest BTU calculation formula for an air conditioner looks like this:
BTU = Square Footage × 20
However, to get a perfectly-sized air conditioner with just right enough cooling power and no energy overspending, you should consider some additional factors. These are:
- Room height.
- Local climate.
- Sun exposure.
- 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 buildings have +10 ft ceilings), you have to add a bit of cooling power in BTU.
There is also a difference if you live in Texas or New York. The local climate in Texas is, 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:
- If you have high walls.
- If you live in a hot climate. Examples: California, Texas, Florida, New Mexico, and so on.
- If the particular room you want to cool down is facing the sun more often than not.
- If you have an above-average size and number of windows.
Example: If you have a 500 sq ft sun cabin near Texas with many glass windows, you should be looking at 10,000 BTU air conditioners (as recommended). It would be best if you were looking at 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 BTUs should our air conditioner have.
The equation for ‘sq ft to BTU‘ is quite simple – multiply the sq ft with 20. That means that a 500 sq ft room needs a 10,000 BTU air conditioner. Of course, do make sure 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.
You should use the BTU calculator when choosing different types of air conditioners, including:
- Mini-split AC units. Example: Mr Cool mini-split units have the highest SEER rating of above 20 EER.
- Portable air conditioners. Here you can check the biggest (up to 15,000 BTU), quietest (below 50 dB), and portable AC with heater units. These are the best portable AC units for apartments, for example.
- Window AC units. Here you can check the biggest (24,000+ BTU), quietest (below 42 dB), and window AC units with heaters. Special kinds of window AC units include casement window AC units, through-the-wall AC units, saddle window AC units, and low-profile window units.
Note: Evaporative coolers and mini personal air coolers do not produce a cooling effect that can be expressed in BTU. They use water evaporation instead of the refrigerant-based system to provide a cooling effect.
You can also check a similar BTU calculator for heating here.
We 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 ones you should take), you can ask in the comments, and we’ll try to give you an answer as soon as possible.