What size air conditioner for 800 sq ft? BTU answer and adjustments
For 800 square feet, the baseline is 16,000 BTU/h (20 BTU per sq ft) — about 1.33 tons or 4.7 kW of cooling. Adjust to 17,600 BTU for a sun-baked room, 14,400 for a shaded one, 20,000 if it is a kitchen, and add 600 BTU per regular occupant beyond two.
| Scenario | Rule | BTU/h |
|---|---|---|
| Baseline room | 800 × 20 | 16,000 |
| Very sunny | +10% | 17,600 |
| Heavily shaded | −10% | 14,400 |
| Kitchen | +4,000 | 20,000 |
| Four regular occupants | +600 × 2 | 17,200 |
Conversions: 12,000 BTU/h = 1 ton = 3.517 kW. 16,000 BTU/h ≈ 1.33 tons ≈ 4.7 kW. Figures are cooling capacity to look for on the spec sheet, not electrical input.
Matching a real machine
In equipment terms, 800 sq ft points to a 12,000–14,000 BTU window unit or a 12k mini-split head. Round to the next available size above your adjusted number — never two sizes up: an oversized unit cools fast, stops before dehumidifying, and leaves the room cold and clammy.
Related: BTU sizing explained, window vs portable, and for whole-house equipment the central AC guide. Metric version: puissance par m² (French).
Frequently asked questions
How many BTU for 800 square feet?
16,000 BTU/h as a baseline (20 BTU/sq ft), 17,600 for a very sunny room, 14,400 for a shaded one, plus 4,000 for a kitchen and 600 per occupant beyond two. That is about 1.33 tons or 4.7 kW.
What size AC unit is that?
A 12,000–14,000 BTU window unit or a 12k mini-split head. For whole-house systems serving several enclosed rooms, a Manual J load calculation replaces this room-level rule.
Is 20 BTU per square foot always right?
It is the room-unit baseline ENERGY STAR and the DOE use; ceiling height above 8 ft, poor insulation and big west glazing push it higher, while a well-insulated shaded room can sit lower. The adjustments above capture the common cases.