What Size Air Conditioner for 800 Square Feet?

A 800 sq ft space (about 28 × 28 ft) needs about 18,000 BTU of cooling, so look for an 18,000 BTU air conditioner. A very sunny room needs 19,800 BTU, and a kitchen 22,000 BTU.

Change any number below to match your project. The ac btu calculator works for any size.

Room size

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How it's worked out

  1. The ENERGY STAR chart lists 700 to 1,000 sq ft at 18,000 BTU per hour.
  2. Adjust for the room: +10% for strong sun, −10% for heavy shade, +600 BTU for each regular occupant past two, +4,000 BTU for a kitchen, and scale up for ceilings over 8 ft.
  3. Pick the nearest common unit size at or just above the result.

800 sq ft: size by room conditions

RoomBTU neededUnit to look for
Normal room18,000 BTU18,000 BTU
Very sunny (+10%)19,800 BTU24,000 BTU
Heavily shaded (−10%)16,200 BTU18,000 BTU
4 people use it (+1,200)19,200 BTU24,000 BTU
Kitchen (+4,000)22,000 BTU24,000 BTU
9 ft ceiling (+12.5%)20,300 BTU24,000 BTU

Don't oversize much. A unit that's too big cools the air quickly and shuts off before it pulls out the humidity, so the room ends up cold and clammy. For an open area this big, a mini split or two smaller units often cool more evenly than one large window unit.

Other common sizes

More detail: What Size AC Do I Need? BTU and Tons by Square Footage