I've seen my R600 cover 3000 sq ft in a midwest 2-story house with open floorplan construction (30mbit+ everywhere). I've seen the same AP cover less than 4 offices (~400 sq ft) in an office with lots of walls, narrow hallways, and 100+ competing neighbor APs (drops down to under 5mbit at those ranges).
It's a huge range and likely won't help to answer your question! What kind of environment are you deploying in, and what is your goal in terms of the speeds you deliver?