BTU per square foot — the quick reference
For cooling, rooms need roughly 20–30 BTU per square foot (this tool uses 25 as the base). For heating, the range is 30–60 BTU per square foot depending on climate and insulation (base 40 here). Kitchens add about 4,000 BTU of cooling load, and every person beyond two adds roughly 600 BTU.
| Room size | Cooling BTU | Window AC size |
|---|---|---|
| 10 × 10 (100 sq ft) | ~2,500–3,000 | 5,000 BTU (smallest sold) |
| 12 × 12 (144 sq ft) | ~3,600–4,300 | 5,000–6,000 BTU |
| 14 × 16 (224 sq ft) | ~5,600–6,700 | 6,000–8,000 BTU |
| 16 × 20 (320 sq ft) | ~8,000–9,600 | 10,000 BTU |
| 20 × 25 (500 sq ft) | ~12,500 | 12,000–14,000 BTU / mini split |
Cooling BTU vs heating BTU — why they differ
The same room needs more BTU to heat than to cool in most of the US, because winter indoor-outdoor temperature differences (up to 70°F) are much larger than summer ones (about 20°F). That is why this calculator switches its base rate between modes instead of using one number. Electric space heaters are rated in watts — divide BTU by 3.412 to convert (1,500 W ≈ 5,100 BTU).
Frequently asked questions
How many BTU do I need for a 12x12 room?
A 12×12 room (144 sq ft) needs about 3,600–4,300 BTU of cooling. The smallest window units sold are 5,000 BTU, which fits perfectly with a little headroom.
How many BTU per square foot?
Use 20–30 BTU per sq ft for cooling (25 is a solid average) and 30–60 BTU per sq ft for heating depending on climate and insulation.
Is higher BTU better for AC?
Only up to the size the room actually needs. A too-powerful window AC cools the air before removing moisture, so the room feels cold but clammy, and the unit cycles constantly.
How many BTU is 1,500 watts?
1,500 W equals about 5,100 BTU/hr — the output of a typical full-size electric space heater on high.