The exact size of an air conditioner for an apartment varies depending on the size of the space and the layout of the apartment. A 500-square-foot room, for example, requires a 12,000 BTU air conditioner while a room with 100 square feet requires a 5,000 BTU unit.
The layout of the apartment is important when determining the best air conditioning solution. Apartments with open floor plans require one large air conditioning unit, while an apartment with multiple small rooms require a smaller air conditioner in each room. For rooms that are sunny, it is necessary to choose an air conditioner with 10 percent greater capacity than recommended for the square footage.