There is a complicated heat/loss formula that needs to be done that takes into account windows, insulation, etc.
A/c tonnage is based on 12,000 btu per ton. Rules of thumb I have heard say a ton per 400, 500, and/or 600 square feet. Have a professional do it instead of taking your pick.
My guess is that you are roughly looking at a 2 1/2 ton and possibly a 3 ton. Get too big and it won't run enough to dehumidify cause it cools too quickly. Get too small and it will run all the time and not cool enough.
Your climate has a lot to do with it also such as temperature and humidity. Good luck.