How Many BTU Per Square Foot Do I Need? (20 BTU Per Sq Ft)

When you’re looking for an air conditioner, you first need to answer what size of an AC unit you need. We all have a home with different square footage, sun exposure, and climate areas.

Luckily, there is a simple rule of thumb for how many BTU per square foot you need.

It’s based on 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.” (DOE, Room Air Conditioners)

Simple answer to ‘how many BTU per square foot’ is 20 BTU per sq ft.

You will probably need more than 20 BTU if you live in sunny Texas or if you have lots of windows. To properly estimate the size of an air conditioner for your square footage, you can use the BTU calculator here.

Based on this rule of thumb, we have calculated how many BTU for 100 square feet to 5,000 square feet you need. Here is a table with summarized BTU requirements:

How Many BTU To Cool 100 to 5,000 Sq Ft (Table)

Square Footage BTU Capacity
How many BTUs for 100 square feet? 2,000 BTU
How many BTUs for 200 square feet? 4,000 BTU
How many BTUs for 300 square feet? 6,000 BTU
How many BTUs for 400 square feet? 8,000 BTU
How many BTUs for 500 square feet? 10,000 BTU
How many BTUs for 600 square feet? 12,000 BTU
How many BTUs for 700 square feet? 14,000 BTU
How many BTUs for 800 square feet? 16,000 BTU
How many BTUs for 900 square feet? 18,000 BTU
How many BTUs for 1000 square feet? 20,000 BTU
How many BTUs for 1100 square feet? 22,000 BTU
How many BTUs for 1200 square feet? 24,000 BTU
How many BTUs for 1300 square feet? 26,000 BTU
How many BTUs for 1400 square feet? 28,000 BTU
How many BTUs for1500 square feet? 30,000 BTU
How many BTUs for 1600 square feet? 32,000 BTU
How many BTUs for 1700 square feet? 34,000 BTU
How many BTUs for 1800 square feet? 36,000 BTU
How many BTUs for 1900 square feet? 38,000 BTU
How many BTUs for 2000 square feet? 40,000 BTU
How many BTUs for 2500 square feet? 50,000 BTU
How many BTUs for 3000 square feet? 60,000 BTU

When you figure out what capacity AC you need, you’ll probably want to buy one. You can check the best AC units in this way:

15 thoughts on “How Many BTU Per Square Foot Do I Need? (20 BTU Per Sq Ft)”

  1. My apartment has 8′ ceilings,faces North. Main room in 12 X 20,, with small (5 X5) kitchen and bath (5 X 6) off a 6 foot hallway, leading to a 7 X 14 sleeping area with window. Total = 450 SF. How many BTU’s do I need? Do I need separate window units for main living area and sleeping area? Thanks.

    • Hello Sidney, for 450 sq ft you would theoretically need 450 sq ft * 20 = 9,000 BTU. However, you are dealing with 4-5 rooms here. 10,000 BTU would be better. We would recommend a 12,000 BTU unit just to be sure.

  2. I have a small 12×18 one room log cabin 8′ walls and a 14′ ceiling peak with very little insulation and big windows all the way across the front, we have tinted the windows and put outdoor curtains across the front porch in an effort to cool it, it has a free standing 14000 BTU Toshiba ac that will not cool it down on peak summer days. what size mini split ac do you recommend for this application. Thanks

    • Hello Bobby, cabins are special cases due to low insulation and high (above 8′ ceiling). For example, you have a 14′ ceiling which is quite extraordinary, and usually theoretical equations to calculate the BTU give a bad estimate. It would be best if you talk to an HVAC specialist who has experience with high ceiling/low insulation spaces. You can contact mini-split HVAC experts for free here.

  3. Hi I live in Jamaica. I have 300 sf bedroom with a 10f ceiling. All the literature says 35 btu per sf is good enough. the salesmen down keep pushing 75 btu/sf on me. I have concrete walls.

    • Hello Tex, the conservative EPA recommendation is 20 BTU per sq ft (given you have 8 ft ceilings). For 10 ft ceilings, 35 sq ft sounds about right. 75 BTU per sq ft is certainly overkill. You’re looking at max. 1 ton (12,000 BTU) unit for 300 sq ft. 75 BTU per sq ft would skyrocket the cooling capacity to about 2 tons. 2 tons for a 300 sq ft bedroom? That’s too much for sure. Hope this helps.

    • Hello Tex I don’t know if you already installed that unit but the technician is right.In Jamaica the calculation used is 65 to 70 based on where on the island you are.Trust me if your in hot parts such as Kingston,Portmore and other hot areas,even in cool areas like mandevile,if you use learn metrics calculation of 20 without a doubt,your unit would be SEVERELY undersized and that’s based on EXPERIENCE!!!!

  4. I have a small cabin in Wisconsin that has a mini split. But there are two small bedrooms up stairs, each is 9 by 7. They have electric heat but no AC. They both have one large casement window. No way to add a window AC unit. I am thinking about adding a two zone ductless. But co corned that the room is so small that any system will just freeze it out. Very good window and we’ll Insulated. Any thoughts

  5. Any thought on efficiency of ductless or ducted systems and size needed. We have 5 rooms in 1200 sq ft house. Any difference in size of btu whether using ductless or ducted?

    • Hello Cynthia, the BTU requirements are the same for ductless and ducted systems. Usually, the ducted systems are bigger houses, and there are both expensive and complex to install. In your case with a 1,200 sq ft house, ductless mini-splits would be the optimum choice. As far as energy efficiency, the mini-splits can be even more energy-efficient than ducted central AC units. Energy efficiency is measured by SEER rating. Most ducted units have up to 20 SEER rating, mini-split units can have 22 SEER rating (10% more efficient).

      In your case, you’re looking at a 30,000 BTU to 40,000 BTU unit with several air handlers to homogeneously cool down all 5 rooms. The perfect solution would be a three-zone ductless mini-split unit with combined cooling output between 30,000 BTU and 40,000 BTU. You can check out our article about these 3-zone mini-splits here. 1. Senville SENA-36HF/T with a 22.5 SEER rating would be a good choice; 4. COOPER AND HUNTER with a 22 SEER rating would actually be an even better one. Hope this helps.


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