A 12,000 BTU air con unit can cool a space between 500sq ft and 550 sq ft of floor space.
There are three types of air conditioners. Portable units are small enough to move between rooms but powerful enough to cool all spaces. While ceiling cassette and split units offer a permanent solution. These must be professionally installed but are quieter than portable ACs, and can even heat rooms more efficiently than central heating.
Although similar in size, portable air conditioners provide more powerful and even air cooling than evaporative air coolers. AC also dehumidify as they cool, however, if humidity isn't a concern and you just need spot cooling, you could also consider a portable and compact air cooler, which cools air using water or ice.