**A 3.5-ton air-conditioning unit cools homes from 1,801 to 2,300 square feet, depending on location.** The unit cools 1,801 to 2,100 square feet in southern states from Georgia to California, and it covers 2,101 to 2,300 square feet in northern states. For existing systems, model numbers reveal the unit capacity.

Manufacturers use a code in the model number of outdoor units instead of listing unit capacity on the air conditioner. If the model number is CKL42-1, for example, the unit is 3.5 tons. The number 42 means the unit is 42,000 British thermal units; when divided by 12,000 Btu per ton, the result is 3.5 tons.

Alternatively, residential load calculations can scientifically determine the proper size air-conditioning unit.