How to estimate AC for a specified area

The BTUs are estimated on the square footage that has to be cooled.

Square footage of home. Cooling hours for your part of the country, even house construction, windows, insulation, blue board, house wrap, tight or loose construction all can make a difference.

My only advise, would be to tell you, bigger is not better. An over sized A/C will cool fine but won't dehumidify the air. Anyone in very hot/humid climates like Florida should consider 2 stage equipment, beware though, 2 story homes with only 1 A/C unit have poor performance on the second floor with staged equipment, because cooler denser air is harder to move with a slower blower in 1st stage.