BTU Chart by Room Size: AC Sizing Chart (Square Feet)
Answer
9,000 BTU for 400 sq ft
Air conditioner capacity by room size, from the Energy Star room AC chart (8 ft ceilings, two people). Very sunny rooms take about 10% more and heavily shaded rooms 10% less.
Free, no sign-upInstant resultsUpdated October 2026
BTU Chart by Room Size
Room size
Shaded
Average
Very sunny
kW
Tons
100 ft²
5,000
5,000
6,000
1.5
0.42
150 ft²
5,000
5,000
6,000
1.5
0.42
200 ft²
6,000
6,000
7,000
1.8
0.50
250 ft²
6,000
6,000
7,000
1.8
0.50
300 ft²
7,000
7,000
8,000
2.1
0.58
350 ft²
8,000
8,000
9,000
2.3
0.67
400 ft²
9,000
9,000
10,000
2.6
0.75
450 ft²
9,000
10,000
11,000
2.9
0.83
500 ft²
11,000
12,000
14,000
3.5
1.00
550 ft²
11,000
12,000
14,000
3.5
1.00
600 ft²
13,000
14,000
16,000
4.1
1.17
700 ft²
13,000
14,000
16,000
4.1
1.17
800 ft²
17,000
18,000
20,000
5.3
1.50
1,000 ft²
17,000
18,000
20,000
5.3
1.50
1,200 ft²
19,000
21,000
24,000
6.2
1.75
1,400 ft²
21,000
23,000
26,000
6.7
1.92
1,500 ft²
22,000
24,000
27,000
7.0
2.00
2,000 ft²
27,000
30,000
33,000
8.8
2.50
Add 600 BTU per person above two and 4,000 BTU for a kitchen. For whole houses use the AC tonnage calculator.
Recommended AC capacity
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How we calculated this
For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer
Find your room's square footage (length × width) and read the BTU for its sun exposure. If you fall between two common unit sizes, take the next one up, but avoid going much larger: an oversized AC short-cycles and removes less humidity.
Frequently asked questions
How many BTU per square foot?
About 20 BTU per square foot for typical rooms. Small rooms need a bit more per square foot, large open spaces a bit less.
What size AC for a 12x12 room?
144 ft² → 5,000 BTU, or 6,000 BTU if it gets strong afternoon sun.