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BTU AC Sizer

Find the right air conditioner size in BTUs for any room, accounting for ceiling height, sunlight, room type and occupants.

AC sizing

Enter the room details. Results update live.

Recommended capacity
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Enter the room area to size the AC.

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The 20 BTU per square foot rule

As a starting point, rooms need about 20 BTU of cooling per square foot. A 400 square foot room therefore starts at 8,000 BTU. The calculator then adjusts that base for ceiling height, sun exposure, kitchens and extra occupants, which all add heat the AC must remove.

Why oversizing is bad

A unit that is too large cools the room so fast it shuts off before removing humidity, leaving the air cold and clammy. It also short cycles, which wears parts faster. Slightly under the calculated size is better than far over it.

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BTU AC Sizer FAQs

How many BTU do I need for a 12x12 room?
A 144 square foot bedroom needs about 5,000 to 6,000 BTU with average sun. Very sunny rooms should go one size up, shaded rooms can go one size down.
Is a bigger BTU air conditioner always better?
No. An oversized unit short cycles, cools unevenly and leaves humidity high. Match the BTU rating to the room size using the calculator above.
Do I need more BTU for a kitchen?
Yes, kitchens add heat from cooking, so add about 4,000 BTU to the room calculation. The calculator includes this when you select kitchen.
Does ceiling height change the BTU needed?
Yes. Taller ceilings mean more air volume to cool, so the calculator scales the result by ceiling height relative to a standard 8 foot ceiling.
What BTU is a 1 ton air conditioner?
One ton of cooling equals 12,000 BTU per hour. A 24,000 BTU unit is a 2 ton system, which is a common size for central air in medium homes.
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