AC BTU calculator: what size air conditioner do I need for my room?
6,000 BTU per hour
180 sq ft · ENERGY STAR row 150 up to 250 sq ft: 6,000 BTU · for a 15 × 12 ft room
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3/8 or 10' 6".
6,000 BTU per hour
180 sq ft · ENERGY STAR row 150 up to 250 sq ft: 6,000 BTU
Source: ENERGY STAR, Room Air Conditioners, Properly Sized Room Air Conditioners: capacity by area to be cooled, with the adjustments for sun, people and kitchens (U.S. EPA), read November 3, 2026. Read the source
A 12 by 15 foot room, 180 square feet, needs a 6,000 BTU per hour room air conditioner by the ENERGY STAR sizing chart (150 up to 250 square feet), 10 percent more if very sunny.
A worked example
A very sunny 13 ft 6 in × 21 ft 9 in family room used by three people needs 8,300 BTU per hour. 293.6 sq ft falls in the 250 up to 300 row, 7,000 BTU. Very sunny adds 10 percent, 7,700, and the third person 600 more: 8,300.
What size AC for a 12 × 12 room?
5,000 BTU: 144 sq ft is in the ENERGY STAR row of 100 up to 150 sq ft. Very sunny, 5,500; in a kitchen, 9,000.
How many BTU per square foot for an air conditioner?
The ENERGY STAR chart goes from about 50 BTU per sq ft in a 100 sq ft room (5,000) to 14 in a 2,400 sq ft space (34,000): bigger spaces take fewer BTU per square foot, so a single per square foot figure overshoots large rooms.
What else it is called
Also searched as an air conditioner size calculator, an AC size calculator, an air conditioner BTU calculator or an AC BTU calculator for room size. For an L shaped room, measure it as two rectangles and add the square feet.
The ENERGY STAR sizing chart
| Room area | Capacity | Very sunny (+10%) | Heavily shaded (−10%) |
|---|---|---|---|
| 100 up to 150 sq ft | 5,000 BTU | 5,500 BTU | 4,500 BTU |
| 150 up to 250 sq ft | 6,000 BTU | 6,600 BTU | 5,400 BTU |
| 250 up to 300 sq ft | 7,000 BTU | 7,700 BTU | 6,300 BTU |
| 300 up to 350 sq ft | 8,000 BTU | 8,800 BTU | 7,200 BTU |
| 350 up to 400 sq ft | 9,000 BTU | 9,900 BTU | 8,100 BTU |
| 400 up to 450 sq ft | 10,000 BTU | 11,000 BTU | 9,000 BTU |
| 450 up to 550 sq ft | 12,000 BTU | 13,200 BTU | 10,800 BTU |
| 550 up to 700 sq ft | 14,000 BTU | 15,400 BTU | 12,600 BTU |
| 700 up to 1,000 sq ft | 18,000 BTU | 19,800 BTU | 16,200 BTU |
| 1,000 up to 1,200 sq ft | 21,000 BTU | 23,100 BTU | 18,900 BTU |
| 1,200 up to 1,400 sq ft | 23,000 BTU | 25,300 BTU | 20,700 BTU |
| 1,400 up to 1,500 sq ft | 24,000 BTU | 26,400 BTU | 21,600 BTU |
| 1,500 up to 2,000 sq ft | 30,000 BTU | 33,000 BTU | 27,000 BTU |
| 2,000 up to 2,500 sq ft | 34,000 BTU | 37,400 BTU | 30,600 BTU |
ENERGY STAR, Properly Sized Room Air Conditioners: BTU per hour by room area, for an 8 ft ceiling. Add 600 BTU for each person over two who regularly uses the room, and 4,000 BTU in a kitchen.
Where the numbers come from
- ENERGY STAR: Room Air Conditioners, “Properly Sized Room Air Conditioners”: 100 up to 150 sq ft, 5,000 BTU per hour; 150 up to 250, 6,000; 250 up to 300, 7,000; 300 up to 350, 8,000; 350 up to 400, 9,000; 400 up to 450, 10,000; 450 up to 550, 12,000; 550 up to 700, 14,000; 700 up to 1,000, 18,000; 1,000 up to 1,200, 21,000; 1,200 up to 1,400, 23,000; 1,400 up to 1,500, 24,000; 1,500 up to 2,000, 30,000; 2,000 up to 2,500, 34,000, for an 8 ft ceiling. Read November 3, 2026. ENERGY STAR guide
- ENERGY STAR adjustments: “If the room is heavily shaded, reduce capacity by 10 percent.” “If the room is very sunny, increase capacity by 10 percent.” “If more than two people regularly occupy the room, add 600 BTUs for each additional person.” “If the unit is used in a kitchen, increase capacity by 4,000 BTUs.” ENERGY STAR guide
- Where the chart leaves it open, this page decides and says so: a row runs from its figure up to the next without including it (150 sq ft is the 150 up to 250 row), the percent goes first and the additions after, and under 100 sq ft it uses the smallest row.
The chart is for room air conditioners and an 8 ft ceiling. It says nothing about mini splits or central air for a whole house, and it stops at 2,500 sq ft, so neither is in this calculator.
By Javier Miralles · Last updated . How this site is made.
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