BTU Calculator
Find the right air conditioner size for a room. Enter the room dimensions and conditions to get the recommended cooling capacity in BTU per hour.
How to use the BTU Calculator
- Enter the room length and width in feet.
- Choose how sunny the room is.
- Enter how many people use it and whether it is a kitchen.
How it works
The base capacity comes from the ENERGY STAR room air conditioner sizing chart (for example, 150–250 sq ft needs about 6,000 BTU/h). It is then adjusted: −10% for a heavily shaded room, +10% for a very sunny room, +600 BTU for each regular occupant beyond two, and +4,000 BTU for a kitchen.
An oversized AC cools quickly but removes less humidity, leaving the room clammy; undersized units run constantly.
ENERGY STAR room AC sizing
| Room area (sq ft) | Capacity (BTU/h) |
|---|---|
| 100–150 | 5,000 |
| 150–250 | 6,000 |
| 250–300 | 7,000 |
| 300–350 | 8,000 |
| 350–400 | 9,000 |
| 400–450 | 10,000 |
| 450–550 | 12,000 |
| 550–700 | 14,000 |
| 700–1,000 | 18,000 |
| 1,000–1,200 | 21,000 |
| 1,200–1,400 | 23,000 |
| 1,400–1,500 | 24,000 |
| 1,500–2,000 | 30,000 |
| 2,000–2,500 | 34,000 |
Frequently asked questions
How many BTU do I need for a 12×12 room?
A 144 sq ft room needs about 5,000 BTU/h in normal conditions.
How many BTU per square foot?
Room AC sizing works out to roughly 20 BTU per square foot for typical rooms.
What does BTU mean?
A British thermal unit is the heat needed to warm one pound of water by 1 °F. AC capacity is given in BTU per hour.