Bigger is not always better. A unit that is too large will not cool an area uniformly and it will cool too quickly causing the unit to turn on and off too frequently. A unit that is too small will run constantly on hot days and still not be able to cool the area adequuately.
In sizing an air conditioner for your home, consider the dimensions of the area to be cooled . An air conditioner generally needs 20 Btu for each square foot of living space. A room that is 15 feet wide by 20 feet long you would calculate: 15×20x20(Btu)=6,000 Btu capacity would be required.