Air Conditioner Size Calculator
The cooling capacity a room needs, in BTU per hour and kW, from its area and conditions
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Gives the cooling capacity a room needs in BTU per hour, kW, kcal/h and refrigeration tons from its floor area, sunlight, number of people and kitchen use. Use it to choose the size of a room or window air conditioner before you shop.
How to use
- Under "Enter", choose "Area" and type the "Room area" with its "Area unit", or choose "Length × width" and enter the room size.
- Set "Sunlight", "People usually in the room" and "Used in a kitchen" under "Room conditions"; "Cooling capacity needed" updates at once.
- Open "How it was calculated" to see the chart row and each adjustment.
- For a whole home, type a "Room name" and press "Add this room to the list" for each room to see the total. The "Cooling capacity unit converter" below converts any value.
How it works
- The base value comes from the ENERGY STAR room air conditioner sizing chart, which assumes an 8 ft ceiling. Only the adjustments from the same guide are applied: heavily shaded −10%, very sunny +10%, 600 BTU/h for each person beyond two, and 4,000 BTU/h for a kitchen.
- Rooms over 2,500 sq ft are outside the chart. Top floors, insulation and heat from electronics are not adjusted for because the guide gives no factor for them.
- 1 kW = 3,412 BTU/h, and one US ton of refrigeration is 12,000 BTU/h. The room list is saved only in this browser on this device.
Questions and answers
- What size air conditioner do I need for a 300 sq ft room?
- A room of 300 up to 350 sq ft needs about 8,000 BTU per hour by the ENERGY STAR chart. Add 10% if the room is very sunny.
- How many BTU do I need per square foot?
- The chart is not a fixed rate per square foot: 150 sq ft needs 6,000 BTU/h, while 1,000 sq ft needs 21,000 BTU/h. Enter your area to get the matching row.
- How do I convert BTU to kW?
- Multiply BTU per hour by 0.000293. For example, 12,000 BTU/h is about 3.52 kW, which is one ton of refrigeration.
- Is a bigger air conditioner better?
- Not always. ENERGY STAR notes that an oversized unit cools the air before it removes humidity, so the room can feel damp. Follow the installer's sizing.