How many BTU does my AC need?
Enter the floor area of the room and tell us about its sun, people and use. See the cooling capacity to look for in a room air conditioner, in BTU per hour and in tons.
- Cooling capacity
- 6,000 BTU/h
A 200 ft² room needs an air conditioner of about 6,000 BTU/h.
- From the area alone
- 6,000 BTU/h
- Tons of cooling
- 0.5
- Cooling in watts
- 1,758 W
Cooling capacity: 6,000 BTU/h. A 200 ft² room needs an air conditioner of about 6,000 BTU/h.
How to calculate
Computes the cooling capacity in BTU per hour for a room air conditioner from the room area, sun, people and kitchen use, by the ENERGY STAR sizing table.
Example with the default inputs (Room area 200 ft², Sun Normal, People 2, Kitchen No): A 200 ft² room needs an air conditioner of about 6,000 BTU/h.
Method: capacity = table value for the area × (0.9 shaded, 1.1 very sunny) + 600 BTU/h for each person over 2 + 4,000 BTU/h for a kitchen
- The table rows run from their lower area up to, not including, the next row’s; the last row includes 2,500 ft².
- The ENERGY STAR table is for room air conditioners in one room. It is not a load calculation for central air, which needs a full load calculation such as ACCA Manual J.
- The adjustments are applied in this order: sun first, as a percent of the table value, then people and kitchen as fixed amounts.
Worked examples
Each example is checked against the calculator on every build.
- Room area 200 ft², Sun Normal, People 2, Kitchen no gives Cooling capacity 6,000 BTU/h, Tons of cooling 0.5.Source: ENERGY STAR sizing table: 150 to 250 ft² needs 6,000 BTU/h
- Room area 400 ft², Sun Very sunny, People 4, Kitchen no gives From the area alone 10,000 BTU/h, Cooling capacity 12,200 BTU/h.Source: ENERGY STAR table: 400 to 450 ft² is 10,000 BTU/h; + 10% for a very sunny room = 11,000; + 600 × 2 extra people = 12,200 (hand calculation in content.mdx)
- Room area 300 ft², Sun Heavily shaded, People 1, Kitchen yes gives From the area alone 8,000 BTU/h, Cooling capacity 11,200 BTU/h.Source: ENERGY STAR table: 300 to 350 ft² is 8,000; − 10% for heavy shade = 7,200; + 4,000 for a kitchen = 11,200 (hand calculation in content.mdx)
- Room area 2,500 ft², Sun Normal, People 2, Kitchen no gives Cooling capacity 34,000 BTU/h.Source: ENERGY STAR table: 2,000 to 2,500 ft² needs 34,000 BTU/h (the last row includes 2,500)
- Room area 322.9 ft², Sun Normal, People 2, Kitchen no gives Cooling capacity 8,000 BTU/h.Source: hand calculation in content.mdx: 30 ÷ 0.09290304 = 322.9 ft², in the 300 to 350 row: 8,000 BTU/h
How it works
- Find the row for the room area in the ENERGY STAR table. Each row runs from its lower area up to, but not including, its upper area; the last row includes 2,500 ft². Areas below 100 ft² or above 2,500 ft² are outside the table. To absorb float noise, the area is multiplied by 1 + 10⁻¹³ before the row is found, so an area typed exactly on a row edge belongs to the upper row.
| Area (ft²) | BTU/h |
|---|---|
| 100 to 150 | 5,000 |
| 150 to 250 | 6,000 |
| 250 to 300 | 7,000 |
| 300 to 350 | 8,000 |
| 350 to 400 | 9,000 |
| 400 to 450 | 10,000 |
| 450 to 550 | 12,000 |
| 550 to 700 | 14,000 |
| 700 to 1,000 | 18,000 |
| 1,000 to 1,200 | 21,000 |
| 1,200 to 1,400 | 23,000 |
| 1,400 to 1,500 | 24,000 |
| 1,500 to 2,000 | 30,000 |
| 2,000 to 2,500 | 34,000 |
- Adjust for sun: × 0.9 for a heavily shaded room, × 1.1 for a very sunny room.
- Add for people: 600 BTU/h for each person over two.
- Add for a kitchen: 4,000 BTU/h.
Tons = BTU/h ÷ 12,000. Watts = BTU/h × 1,055.05585262 ÷ 3,600; this is the heat the unit removes, not the electricity it uses.
Areas in square metres convert with 1 ft² = 0.09290304 m².
Worked examples by hand
A 200 ft² bedroom, normal sun, two people. 200 ft² is in the 150 to 250 row: 6,000 BTU/h, or 0.5 ton.
A very sunny 400 ft² living room used by four people. The row is 400 to 450: 10,000. × 1.1 = 11,000. Two people over two add 1,200: 12,200 BTU/h.
A shaded 300 ft² kitchen, one person. The row is 300 to 350: 8,000. × 0.9 = 7,200. The kitchen adds 4,000: 11,200 BTU/h.
2,500 ft². The last row includes its upper end: 34,000 BTU/h.
30 m². 30 ÷ 0.09290304 = 322.9 ft², in the 300 to 350 row: 8,000 BTU/h.
Other questions people ask
How many BTU do I need per square foot?
ENERGY STAR sizes room air conditioners by area bands rather than a single rate: 150 to 250 ft² needs 6,000 BTU/h, 350 to 400 ft² 9,000, 450 to 550 ft² 12,000. That is between about 14 and 50 BTU/h per square foot, falling as rooms get larger.
What adjustments does ENERGY STAR make?
Reduce the capacity by 10% for a heavily shaded room and increase it by 10% for a very sunny one. Add 600 BTU/h for each person over two who regularly use the room, and 4,000 BTU/h if the unit is in a kitchen.
Why not just buy a bigger air conditioner?
ENERGY STAR notes that an oversized unit cools the room before it has removed enough humidity, so the cool, moist air feels damp and clammy. Match the size to the room.
What is a ton of air conditioning?
One ton of refrigeration is 12,000 BTU per hour (NIST SP 811). A 6,000 BTU/h unit is half a ton.
How do I find my room’s area?
Multiply the length by the width of the floor. A room 12 ft by 16 ft is 192 ft². For an L-shaped room, split it into rectangles and add them.
Can I use this for central air?
No. The table is for room air conditioners in one room. Sizing central air for a house takes a full load calculation that counts insulation, windows, climate and duct losses, such as ACCA Manual J.