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You can either go for a 1 ton AC or a 1.5 ton AC depending upon the amount of light that enters the room, area and direction of windows, the floor on which your room is situated, number of people occupying the room and the number of lights.
If you are talking about a whole house AC unit the sizes can also vary considerably and there are many variables to consider. A typical new home of about 1400 ft. sq. located in the desert southwest area of the US would have a 3 Ton AC unit or 36,000 BTU ground or packaged AC unit. 3500 watts - Central Air Conditioner.