I've read in poultry books that the rule of thumb for runs is 10 sq ft per bird. Using that formula I have enough room for for 160 more birds. The 25 in my flock have completely denuded the ground closest to the coop. Chickens don't graze like cattle they pluck plants, often root as well. Sooner or later where ever you have them will turn into a lunar landscape. It doesn't matter how large an area you have for them, so spots will wind up bare.