3x6 is 18 square feet, how tall is the coop. I don't know why, people always talk square footage, but space is three dimensional. It depends on your chickens, and what your set up exactly looks like, a rule of thumb is 4 sq feet per bird, so with 18 sq feet, you should have 4-5 birds. I agree, the 7th bird will cause more trouble than it is worth.