2 sq feet per chicken in some books I've read and 1 1/2 sq feet in others. It also depends on how much room you have in your outside run. The 5 sq foot thing is probable for chickens with no outside run.
They say about 4 or 5 square feet per bird in the coop. And this is floor space, not including roost bars or nest boxes. 10 square feet per bird in the run. But the more room the better. Chickens go off on each other very easily when cramped in. So I can't stress enough to give them plenty of room and not to squeeze them in.
Here is an article in our learning center on space requirements...
I have an almost 200 sq ft outdoor run. My nesting boxes measure 12"x12"x16" and an 18"x13' "porch" on the outside of the nesting boxes. How many chickens would you believe is appropriate for this space? Do you think my nesting boxes are too small?
Hello and Welcome To BYC! X3 on TwoCrows post, good luck with your coop build!
mschickenlady, I am not quite following how big your actual coop is? Do you have an open air coop that is not enclosed on most sides? How much covered space, roosts etc do you have? 12x12x16" nest boxes are fine for most standard birds, if you have some real big breeds you might want to go larger.