Check with the sales people in the store for your area and climate. I would say a 10 or 12,000 btu would do it, if you are only going to buy 1 unit.
In a typical residential application, your space is probably divided into different rooms. In that case, it is difficult to get cool air from one room to another. In that situation you would want multiple air conditioners. They usually do not come in a size less than 5,000 btu's per hour. So, to achieve enough total cooling, you will probably want two or more small air conditioners, one in the living room and one in each bedroom.
24,000 btu's
600 BTU/ ft is what i have been told.
18,000-21,000 BTU's
36000 Btu
420. Get 450 to be safe.
To determine the BTU needed for a room, a common rule of thumb is to allocate about 20 BTU per square foot. For a 108-square-foot room, this would be approximately 2,160 BTU (108 sq ft x 20 BTU/sq ft). However, factors such as ceiling height, room insulation, number of windows, and occupancy can affect this calculation, so adjustments may be necessary for optimal comfort.
450 sq ft = 64,800 sq inches.
2500sq ft in northern climate
450 sq. ft.
14000BTU
700 to 1000
30' x 12'