What Size AC for 300 Sq Ft?
A 300 sq ft space needs about 6,000 BTU/h of cooling (0.5 tons), so the nearest size is 6,000 BTU. This assumes an 8 ft ceiling and average sun. It is a rule of thumb (20 BTU per sq ft), not an engineered load.
AC size for 300 sq ft by situation
| Scenario | BTU/h | Tons | Suggested size |
|---|---|---|---|
| Heavily shaded (−10%) | 5,400 | 0.45 | 6,000 BTU |
| Average sun, 8 ft ceiling | 6,000 | 0.5 | 6,000 BTU |
| Very sunny (+10%) | 6,600 | 0.55 | 8,000 BTU |
| Kitchen (+4,000 BTU) | 10,000 | 0.83 | 10,000 BTU |
| 9 ft ceilings (+12.5%) | 6,750 | 0.56 | 8,000 BTU |
| 10 ft ceilings (+25%) | 7,500 | 0.63 | 8,000 BTU |
| Hot climate (+10%) | 6,600 | 0.55 | 8,000 BTU |
Rule-of-thumb figures for a two-person space; each extra person over 2 adds about 600 BTU.
How it is calculated
300 sq ft × 20 BTU × (8 ÷ 8) = 6,000 BTU/h
6,000 ÷ 12,000 = 0.5 tons
Sunny: 6,000 × 1.1 = 6,600 · Kitchen: 6,000 + 4,000 = 10,000
Which type of AC for 300 sq ft?
- Window or portable unit – A 6,000 BTU window unit fits a room this size and runs on a standard 115V outlet. Portable units are rated lower in practice, so buy one rated a step or two above 6,000 BTU.
- Mini-split – Only worth it if you want quiet operation, no blocked window, or heating too. The smallest ductless heads are around 9,000 BTU, which is more than this room needs, so check for a low-minimum-capacity model.
Frequently asked questions
How many BTU do I need for 300 square feet?
About 6,000 BTU/h for an 8 ft ceiling in average conditions (300 × 20). That is 0.5 tons, so the closest unit is 6,000 BTU.
Is 6,000 BTU enough for 300 sq ft if the room is sunny?
A very sunny space needs about 6,600 BTU, so 8,000 BTU is recommended – a step different from the 6,000 BTU for average sun.
What if the 300 sq ft space has 10 ft ceilings?
The load rises 25% to 7,500 BTU, so choose 8,000 BTU instead of 6,000 BTU. Volume matters, not just floor area.