I had fully fenced (including top) 10 square feet per chicken prior to purchasing my birds as that seemed to be the magic number that people mentioned repeatedly. It's now been a year of them living in their coop/run. They do not free range. They are full grown. I feel this is not enough space for them and have plans for expansion this summer, but not for more birds, just for more run space for the existing birds. After a year I feel their 4 square feet each in the coop has been adequate, but in the run full time, 10 square feet per bird is not really enough.