That is some peoples' rule of thumb, although it is usually cited as a MINIMUM not as an optimum target.
Other people have different rules of thumb.
A whoooole lot depends on what your goals/standards/philosophies are. Your climate matters somewhat too.
If you are in the more-coastal part of southern VA you are close to being plausible for "roosting space only" if you really, really wanted to... although it would require you to have a good big safe hygeinic interesting place for them to spend their daytime hours, preferably with lots of shade for summer and at least partly roofed for rainy days.
Note that in my experience (and I am talking about normal circumstances here, NOT having chickens shut up in coop if you think the weather is too bad) they really do behave DIFFERENTLY at 4 sq ft apiece (plus run) than at larger allowances like 10-15 sq ft apiece (plus run). How much this matters to you will differ among people of course.
I wouldn't suggest less than 8 sq ft per chicken in the run, and lots more is lots better (although there is obviously a tradeoff between size of run and how predatorproof you can make it, not to mention price)
Good luck, have fun,
Pat