My current coop, intended for 4 chickens, is 4 feet wide by 4 feet long by approximately 4 feet tall and I think it's as small as a chicken coop should ever be made.
I currently have 5 POL pullets in it and am watching for signs of trouble while we're in the process of salvaging wood to build the new, MUCH larger coop (getting the hardware cloth may be the hardest part).
It helps that I have a 600+ square foot pen (Premier1 electric poultry netting), and live in a mild climate where they are never restricted to their coop by weather (they actually did come out between rain bands during the hurricanes we had this summer).
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