Coop Space per Bird
As a baseline, standard-size breeds need at least 3-4 square feet of enclosed coop floor space per bird if they'll also have outdoor run access, and closer to 8-10 square feet per bird if they'll be coop-confined most of the time (say, in a cold climate with limited winter outdoor access). Bantam breeds need roughly half that. Size for your maximum expected flock, not your starting flock; most keepers add birds over time, and it's harder to expand a coop later than to build bigger up front.
Run Space per Bird
The outdoor run needs considerably more room than the coop itself: plan on at least 8-10 square feet per bird, and 15+ square feet per bird if the birds won't be free-ranging elsewhere during the day. Birds crammed into a too-small run are far more prone to pecking-order aggression and feather picking; if space is tight, adding vertical elements like perches and platforms helps birds make better use of what they have.
Nesting Boxes: How Many You Actually Need
One nesting box per 3-4 hens is sufficient; hens share and often prefer the same one or two 'popular' boxes even when others sit empty. Standard box dimensions run roughly 12x12x12 inches for standard breeds, positioned lower than the roosting bars so birds aren't tempted to sleep in the boxes (which leads to dirty eggs), and lined with a few inches of bedding.
Roosting Bar Space
Allow 8-10 inches of linear roosting bar space per standard-size bird (about 6 inches for bantams), and use a flat-topped bar (a 2x4 laid flat works) rather than a round dowel, since flat bars let birds tuck their feet under their bodies for warmth in cold weather. Roosts should sit higher than the nesting boxes; chickens instinctively sleep at the highest point they can reach.
Ventilation and Predator-Proofing
A coop needs year-round ventilation up near the roofline (above roost height, so it doesn't create a direct draft on sleeping birds) to keep ammonia from building up and causing respiratory illness, even in cold climates; sealing a coop too tight for winter is a common and serious mistake. For predator-proofing, use hardware cloth (not chicken wire, which larger predators can tear through) on every opening, bury or apron the run's perimeter fencing at least 12 inches to stop diggers, and use a locking mechanism predators can't figure out, since raccoons in particular are surprisingly good at opening simple latches.
Frequently asked questions
How many chickens can a 4x8 coop hold?
A 4x8 coop (32 sq ft) comfortably houses about 8-10 standard-size birds at 3-4 sq ft per bird, assuming outdoor run access. Cut that to about 4-5 birds if they'll be coop-confined most of the time.
How many nesting boxes do I need for 12 hens?
Plan on 3-4 nesting boxes for a flock of 12 hens, using the roughly 1-box-per-3-4-hens ratio. More boxes than that usually go unused, since hens favor a couple of preferred spots anyway.
Can I use chicken wire for the run?
Standard chicken wire keeps chickens in but doesn't reliably keep predators out. Hardware cloth (welded wire mesh, typically 1/2 inch openings) is the standard for any run or coop opening exposed to raccoons, dogs, or other predators.
Do chickens need a heated coop in winter?
Most cold-hardy breeds don't need supplemental heat and tolerate temperatures well below freezing as long as the coop stays dry, draft-free at bird level, and properly ventilated above roost height. Heat lamps introduce a real fire risk and are generally discouraged by poultry-keeping guidance.