Air Conditioner BTU Calculator
This air conditioner BTU calculator tells you what size room AC a space needs. Enter the room's square footage, how sunny it is, how many people normally use it and whether it is a kitchen. The result is the cooling capacity in BTU per hour, based on the ENERGY STAR room air conditioner sizing chart, with the same figure in kilowatts for units rated in kW.
Updated
Results
- Chart value before adjustments (BTU/h)ENERGY STAR chart for this area
- Area used (sq ft)
Results are estimates. See the methodology below.
How to use the calculator
- Keep Imperial (sq ft) selected and enter the floor area of the room. For a rectangular room, multiply length by width; a 12 × 15 ft bedroom is 180 sq ft. Our square footage calculator handles L-shaped rooms.
- Choose the sun exposure: heavily shaded, normal, or very sunny (large windows facing the afternoon sun, for example).
- Enter the number of people who regularly use the room at the same time.
- Tick Kitchen if the unit will cool a kitchen, where the stove and appliances add heat.
The calculator shows the recommended capacity in BTU/h and kW, the base figure from the chart before adjustments, and the area it used.
How the calculation works
The calculator looks up your area in the ENERGY STAR sizing chart for room air conditioners:
| Area (sq ft) | Capacity (BTU/h) |
|---|---|
| up to 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 |
It then applies the ENERGY STAR adjustments in this order:
- Heavily shaded: −10%. Very sunny: +10%.
- Occupants: +600 BTU/h for each person above two.
- Kitchen: +4,000 BTU/h.
Kilowatts = BTU/h ÷ 3,412.14, since NIST gives 1 BTU/h = 0.2930711 W. An area exactly on a boundary, such as 250 sq ft, gets the smaller capacity.
Assumptions
ENERGY STAR calculates the chart for an 8 ft ceiling. The calculator sizes one room at a time and stops at 2,500 sq ft, the top of the chart. It does not account for insulation, climate zone or the number and size of windows.
Worked examples
1. Bedroom, 12 × 15 ft
180 sq ft, normal sun, two people: 6,000 BTU/h (1.76 kW). If the same room is very sunny, the result rises to 6,600 BTU/h.
2. Sunny living room, 400 sq ft, four people
The chart gives 9,000 BTU/h. Very sunny adds 10%, and two extra people add 1,200 BTU/h: 11,100 BTU/h (3.25 kW).
3. Kitchen, 200 sq ft, three people
Base 6,000 BTU/h, plus 600 for the third person and 4,000 for the kitchen: 10,600 BTU/h. The kitchen adjustment alone adds two-thirds of the chart value for the area.
4. Shaded den, 500 sq ft
Base 12,000 BTU/h minus 10% for heavy shade: 10,800 BTU/h.
Choosing a unit from the result
Room air conditioners are sold in fixed capacities, so compare the result with the BTU rating of the models you are considering. Bigger is not better: ENERGY STAR notes that an oversized unit cools the room before it has a chance to remove the humidity, leaving it feeling damp and clammy, and that it costs more to buy and wastes energy.
Installation matters as much as size. ENERGY STAR advises keeping the unit level so the drain works and using the insulation materials supplied, since a poorly installed unit leaks air.
Frequently asked questions
How many BTUs do I need for a 12 × 12 room?
A 12 × 12 ft room is 144 sq ft. With normal sun and up to two people, the chart gives 5,000 BTU/h. Add 10% if the room is very sunny and 600 BTU/h for each extra regular occupant.
How many square feet does a 10,000 BTU air conditioner cool?
In the ENERGY STAR chart, 10,000 BTU/h matches 400 to 450 sq ft under normal conditions. A sunny room or more occupants lowers the area it can handle; a heavily shaded room raises it.
What is a ton of air conditioning?
A ton of refrigeration is 12,000 BTU/h, about 3.52 kW. The term is mostly used for central systems and mini-splits; window and portable units are usually labeled in BTU/h.
Why does a kitchen need so much more?
Cooking appliances release a lot of heat into a small space. ENERGY STAR adds 4,000 BTU/h when the unit is used in a kitchen, regardless of the room size.
What if my ceilings are higher than 8 ft?
The chart assumes 8 ft ceilings and has no correction for taller rooms, which hold more air. For vaulted or very high ceilings, treat the result as a lower bound and ask an HVAC contractor.
Can I use this to size central air for a whole house?
No. The chart is for room air conditioners cooling a single space. Central systems are sized with a load calculation that considers insulation, windows, ducts and local climate.
Sources
This is an estimate for a single room based on the ENERGY STAR chart. For whole-home systems, unusual layouts or high ceilings, get a load calculation from a qualified HVAC professional.