What Size AC Do I Need? BTU and Tons by Square Footage
A small room up to 150 sq ft, like a 12 × 12 ft bedroom, needs a 5,000 BTU room air conditioner, and a 450 to 550 sq ft living room needs 12,000 BTU. For central air, a rough guide is 1 ton (12,000 BTU) for every 500 to 600 sq ft, so a 2,000 sq ft house usually lands around 3.5 to 4 tons. The AC BTU calculator does the room math for you, including sun and ceiling height.
Room air conditioner size chart
This is the ENERGY STAR sizing chart used for window, portable and through-the-wall units.
| Room area (sq ft) | Cooling capacity |
|---|---|
| 100–150 | 5,000 BTU |
| 150–250 | 6,000 BTU |
| 250–300 | 7,000 BTU |
| 300–350 | 8,000 BTU |
| 350–400 | 9,000 BTU |
| 400–450 | 10,000 BTU |
| 450–550 | 12,000 BTU |
| 550–700 | 14,000 BTU |
| 700–1,000 | 18,000 BTU |
| 1,000–1,200 | 21,000 BTU |
| 1,200–1,400 | 23,000 BTU |
| 1,400–1,500 | 24,000 BTU |
| 1,500–2,000 | 30,000 BTU |
| 2,000–2,500 | 34,000 BTU |
Common room sizes
| Room | Sq ft | Chart size |
|---|---|---|
| 10 × 10 ft | 100 | 5,000 BTU |
| 12 × 12 ft | 144 | 5,000 BTU |
| 12 × 14 ft | 168 | 6,000 BTU |
| 15 × 20 ft | 300 | 7,000 BTU |
| 20 × 20 ft | 400 | 9,000 BTU |
| 20 × 25 ft | 500 | 12,000 BTU |
So a 12,000 BTU unit covers about 450 to 550 sq ft, and an 8,000 BTU unit covers about 300 to 350 sq ft.
Adjust for your room
- Very sunny room: add 10%.
- Heavily shaded room: take off 10%.
- More than two people regularly in the room: add 600 BTU per extra person.
- Kitchen: add 4,000 BTU for the heat from cooking.
- Ceilings over 8 ft: scale up by the height, e.g. 10 ft ceilings need 25% more.
Then pick the nearest size you can buy. Going a little over is fine; going much bigger is not. An oversized unit cools the air fast and shuts off before it removes the humidity, leaving the room cold and clammy.
Central air size by house square footage
Central AC is sold in tons, and 1 ton is 12,000 BTU per hour. Use the lower figure for mild climates and well-insulated houses, and the higher figure for hot, sunny climates or older, leaky houses.
| House size | Typical AC size | BTU per hour |
|---|---|---|
| 1,000 sq ft | 2 tons | 24,000 BTU |
| 1,200 sq ft | 2 to 2.5 tons | 24,000–30,000 BTU |
| 1,400 sq ft | 2.5 to 3 tons | 30,000–36,000 BTU |
| 1,500 sq ft | 2.5 to 3 tons | 30,000–36,000 BTU |
| 1,800 sq ft | 3 to 4 tons | 36,000–48,000 BTU |
| 2,000 sq ft | 3.5 to 4 tons | 42,000–48,000 BTU |
| 2,500 sq ft | 4.5 to 5 tons | 54,000–60,000 BTU |
| 3,000 sq ft | 5 tons | 60,000 BTU |
Residential systems top out at 5 tons, so large houses often get two systems or a zoned setup. These numbers are for budgeting and sanity checks. Before buying central air, ask the contractor for a Manual J load calculation, which accounts for insulation, windows, orientation and local weather. A good contractor does one anyway.
Mini splits and garages
Size a mini split head the same way as a room unit: use the room chart for the space it serves. Garages are usually poorly insulated, so for a two car garage of around 400 to 500 sq ft, plan on the upper end of the chart (12,000 BTU or more), especially if the door faces the sun.