Most quotes are for 1) Chickens who live just within a coop or 2) Chickens who get to free range for parts of a day or 3) chickens who get to go out in a run. So, one of my sources say this:
"Figuring coop space per chicken really depends on how big your chickens are and how often you allow them outside in a run or to free range. The more free ranging or confined ranging you allow, the smaller the coop needs to be. At night, chickens take up very little space in the coop (1 Sq. Foot). They perch on a bar and fall asleep. If your chickens are only using the house at night, then they may need a smaller square footage,.
I recommend at least 10 square feet per bird. If a bird is living in a coop with a run attached, it should have an absolute minimum of 10 sq ft, 5 sq ft inside and 5 sq ft outside. An attached chicken run should be as big as your space allows. The smaller the area, the more the chickens will suffer from pests and social struggles"
