How Many BTU Per Square Foot Do I Need? (Calculation Explained)

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

12 thoughts on “How Many BTU Per Square Foot Do I Need? (Calculation Explained)”

  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.

  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


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