Home › BTU calculator
BTU Calculator: What Size Air Conditioner Do I Need?
Find the right size window or mini-split air conditioner for a room, in BTU and tons, based on room size, ceiling height, sun, people and whether it's a kitchen.
Air conditioner size by room size
This is the sizing chart ENERGY STAR publishes for room air conditioners:
| Room area | Cooling capacity |
|---|---|
| 100 to 150 sq ft | 5,000 BTU |
| 150 to 250 sq ft | 6,000 BTU |
| 250 to 300 sq ft | 7,000 BTU |
| 300 to 350 sq ft | 8,000 BTU |
| 350 to 400 sq ft | 9,000 BTU |
| 400 to 450 sq ft | 10,000 BTU |
| 450 to 550 sq ft | 12,000 BTU |
| 550 to 700 sq ft | 14,000 BTU |
| 700 to 1,000 sq ft | 18,000 BTU |
| 1,000 to 1,200 sq ft | 21,000 BTU |
| 1,200 to 1,400 sq ft | 23,000 BTU |
| 1,400 to 1,500 sq ft | 24,000 BTU |
| 1,500 to 2,000 sq ft | 30,000 BTU |
| 2,000 to 2,500 sq ft | 34,000 BTU |
Adjustments
- Heavily shaded room: reduce capacity by 10%.
- Very sunny room: increase capacity by 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 above 8 ft: we scale capacity up with the room's volume.
Why not just buy a bigger unit?
An oversized air conditioner cools the room quickly and shuts off before it has removed the humidity, leaving the room cold and clammy, and it cycles on and off more, which wastes energy. An undersized unit runs nonstop and can't keep up on hot days. Aim for the size the chart gives.
One ton of cooling is 12,000 BTU per hour. For a whole house, central air is sized with a Manual J load calculation, which a licensed HVAC contractor should do.
Frequently asked questions
What size AC do I need for a 12x12 room?
A 144 sq ft room needs about 5,000 BTU. Use 6,000 BTU if it gets lots of sun.
How many square feet does 12,000 BTU cool?
About 450 to 550 sq ft, according to the ENERGY STAR sizing chart.