How many square feet per chicken in a pen?

A pen can be as large as you want to make it, but should provide 10 sq. ft. per bird at a minimum. A coop, which shelters the birds at night or in inclement weather should provide 3 to 5 sq. ft. per bird or as much as 10 sq. ft. per bird if you have the space. If birds are too crowded, behavior problems such as pecking and cannibalism can arise.