The first table is that chart as published; the second applies it to common room sizes so you can read off an answer. For a room of any other size or shape, use the BTU calculator, which applies the same steps.
The ENERGY STAR sizing chart
Find the band that contains your room's floor area, length times width. The capacity beside it is the starting point before any adjustments.
| Area to be cooled | Capacity needed, BTU per hour | Source |
|---|---|---|
| 100 up to 150 sq ft | 5,000 | ENERGY STAR |
| 150 up to 250 sq ft | 6,000 | ENERGY STAR |
| 250 up to 300 sq ft | 7,000 | ENERGY STAR |
| 300 up to 350 sq ft | 8,000 | ENERGY STAR |
| 350 up to 400 sq ft | 9,000 | ENERGY STAR |
| 400 up to 450 sq ft | 10,000 | ENERGY STAR |
| 450 up to 550 sq ft | 12,000 | ENERGY STAR |
| 550 up to 700 sq ft | 14,000 | ENERGY STAR |
| 700 up to 1,000 sq ft | 18,000 | ENERGY STAR |
| 1,000 up to 1,200 sq ft | 21,000 | ENERGY STAR |
| 1,200 up to 1,400 sq ft | 23,000 | ENERGY STAR |
| 1,400 up to 1,500 sq ft | 24,000 | ENERGY STAR |
| 1,500 up to 2,000 sq ft | 30,000 | ENERGY STAR |
| 2,000 up to 2,500 sq ft | 34,000 | ENERGY STAR |
The chart assumes a ceiling of 8 ft. A taller room may need more capacity.
Adjustments for sun, people and kitchens
- Heavily shaded room: reduce the capacity by 10 percent.
- Very sunny room: increase the capacity by 10 percent.
- More than 2 people regularly in the room: add 600 BTU per hour for each extra person.
- Unit used in a kitchen: add 4,000 BTU per hour.
- Then round the total down to the nearest thousand and look for a unit of that size.
Sizes for common rooms
The table applies the chart and the adjustments to typical bedrooms, living rooms and open-plan spaces, so you can compare sizes at a glance. Add occupants beyond the chart's allowance yourself, or use the calculator.
| Room | Floor area, sq ft | Heavily shaded | Average | Very sunny | Kitchen, average sun |
|---|---|---|---|---|---|
| 10 x 10 ft | 100 | 5,000 | 5,000 | 5,000 | 9,000 |
| 10 x 12 ft | 120 | 5,000 | 5,000 | 5,000 | 9,000 |
| 12 x 12 ft | 144 | 5,000 | 5,000 | 5,000 | 9,000 |
| 12 x 14 ft | 168 | 5,000 | 6,000 | 6,000 | 10,000 |
| 12 x 16 ft | 192 | 5,000 | 6,000 | 6,000 | 10,000 |
| 14 x 16 ft | 224 | 5,000 | 6,000 | 6,000 | 10,000 |
| 15 x 20 ft | 300 | 6,000 | 7,000 | 7,000 | 11,000 |
| 16 x 20 ft | 320 | 7,000 | 8,000 | 8,000 | 12,000 |
| 20 x 20 ft | 400 | 8,000 | 9,000 | 9,000 | 13,000 |
| 20 x 25 ft | 500 | 10,000 | 12,000 | 13,000 | 16,000 |
| 20 x 30 ft | 600 | 12,000 | 14,000 | 15,000 | 18,000 |
| 25 x 30 ft | 750 | 16,000 | 18,000 | 19,000 | 22,000 |
Our arithmetic from the ENERGY STAR chart and adjustments, for up to 2 regular occupants, rounded down to the nearest thousand as ENERGY STAR advises and never below the smallest size in the chart. Values are BTU per hour.
Why not buy a bigger unit?
ENERGY STAR warns that an oversized unit costs more to buy, wastes energy and does not cool any better. Because it reaches the set temperature quickly, it shuts off before it has removed much humidity, and the room feels cold and damp.
These charts are for single rooms. Central air for a whole house is sized by a contractor with a load calculation that looks at insulation, windows and climate; the square footage calculator helps with the floor areas, but not with that calculation.
Common questions
What size air conditioner do I need for a 12x12 room?
A 12x12 room is 144 square feet, which falls in the first band of the ENERGY STAR chart; the second table shows the size for each sun setting and for a kitchen.
Do higher ceilings need a bigger air conditioner?
The ENERGY STAR chart assumes a ceiling of 8 ft. A taller room holds more air, so it may need more capacity than the chart gives.
How many BTU per square foot do I need?
The ENERGY STAR chart works in bands of floor area rather than a fixed rate per square foot, and its adjustments matter as much as the area. Use the chart, or the BTU calculator, rather than a per-square-foot rule.
Using these figures
You are welcome to cite the tables on this page. Please link to this page as the source, and check the maker's current data sheet before you rely on a single figure.