What Size AC for 800 Sq Ft?
A 800 sq ft space needs about 16,000 BTU/h of cooling (1.33 tons), so the nearest size is 18,000 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 800 sq ft by situation
| Scenario | BTU/h | Tons | Suggested size |
|---|---|---|---|
| Heavily shaded (−10%) | 14,400 | 1.2 | 18,000 BTU |
| Average sun, 8 ft ceiling | 16,000 | 1.33 | 18,000 BTU |
| Very sunny (+10%) | 17,600 | 1.47 | 18,000 BTU |
| Kitchen (+4,000 BTU) | 20,000 | 1.67 | 24,000 BTU |
| 9 ft ceilings (+12.5%) | 18,000 | 1.5 | 18,000 BTU |
| 10 ft ceilings (+25%) | 20,000 | 1.67 | 24,000 BTU |
| Hot climate (+10%) | 17,600 | 1.47 | 18,000 BTU |
Rule-of-thumb figures for a two-person space; each extra person over 2 adds about 600 BTU.
How it is calculated
800 sq ft × 20 BTU × (8 ÷ 8) = 16,000 BTU/h
16,000 ÷ 12,000 = 1.33 tons
Sunny: 16,000 × 1.1 = 17,600 · Kitchen: 16,000 + 4,000 = 20,000
Which type of AC for 800 sq ft?
- One large or two small window units – At 16,000 BTU, one big window unit rarely cools an open 800 sq ft space evenly. Two units (about 8,000 BTU each) in different rooms work better.
- Mini-split – A single 18,000 BTU mini-split suits an open-plan space; for several closed rooms use a multi-zone system.
- Central AC – If the home has ducts, this is about 1.5 tons, but have the load calculated before choosing.
Frequently asked questions
How many BTU do I need for 800 square feet?
About 16,000 BTU/h for an 8 ft ceiling in average conditions (800 × 20). That is 1.33 tons, so the closest unit is 18,000 BTU.
Is 18,000 BTU enough for 800 sq ft if the room is sunny?
A very sunny space needs about 17,600 BTU, so 18,000 BTU is recommended – the same size as the average case.
What if the 800 sq ft space has 10 ft ceilings?
The load rises 25% to 20,000 BTU, so choose 24,000 BTU instead of 18,000 BTU. Volume matters, not just floor area.