Different people do it different ways of course.
Commercial layers in cages get less than 2 sq ft per hen and that is their *whole entire world*.
Books oriented towards keeping chickens in industry-like conditions (caged layers) suggest 2-4 sq ft per hen, any run space is considered a luxury.
Books and people oriented to keeping chickens "compactly" but in better conditions than the above, so there is less stress and cannibalism and such, tend to recommend 3-4 sq ft per hen indoors plus a run of 6-10 sq ft per hen.
People whose chickens free-range all day and 365 days per year in an always-pleasant climate may have 2 sq ft indoors per hen, but essentially unlimited space outdoors.
I live up here where many chickens are unamused by the outdoor weather for 4-5 months a year, and also I have seen the difference in how chickens act at 4 sq ft per chicken vs lots more, and I have 15 sq ft per chicken indoors plus runs that size or bigger (and I wish they were even bigger).
Obviously I'd strongly argue for giving them as much space as possible, anywhere they are confined or will choose to confine themselves, with 4 sq ft per hen being marginally sufficient but really not ideal IMHO -- but certainly there are lots of different opinions on the subject, and many people with healthy chickens in various size situations.
Good luck, have fun,
Pat
