A:There are other things you may have to take into account other than size such as local climate ,how many windows and size of the windows in your home the level of insulation your home has and other factors. This site gives you an online estimate in less than a minute. I am not sure how reliable it is but it is worth taking a stab at and at least getting an initial idea:
http://www.airconditioninghelper.com/size.htm
