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 (such as in cold climates with limited winter outdoor access). Bantam breeds need roughly half that. Always size for your maximum expected flock, not your starting flock, since most keepers add birds over time and retrofitting a coop is harder than building slightly larger upfront.
Run space per bird
The outdoor run needs considerably more space than the coop itself: plan at least 8-10 square feet per bird for a run, and 15+ square feet per bird if the birds won't be free-ranging elsewhere during the day. Birds confined to an undersized 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 use the run more efficiently.
Nesting boxes: how many you actually need
One nesting box per 3-4 hens is sufficient; hens will happily share and often prefer the same one or two 'popular' boxes even when others are available. Standard box dimensions are roughly 12x12x12 inches for standard breeds, positioned lower than the roosting bars so birds don't try to sleep in the boxes (which leads to soiled 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), using a flat-topped bar (like a 2x4 laid flat) rather than a round dowel, since flat bars let birds cover their feet with their bodies for warmth in cold weather. Roosts should be higher than nesting boxes, since chickens instinctively want to sleep at the highest available point.
Ventilation and predator-proofing
A coop needs year-round ventilation near the roofline (above roost height, to avoid direct drafts on sleeping birds) to prevent ammonia buildup and respiratory illness, even in cold climates; sealing a coop too tightly for winter is a common and serious mistake. For predator-proofing, use hardware cloth (not chicken wire, which larger predators can tear) on all openings, bury or apron the run's perimeter fencing at least 12 inches to stop digging predators, and secure a locking mechanism predators can't manipulate, since raccoons in particular can open 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 they also have outdoor run access; reduce 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 for 3-4 nesting boxes for a flock of 12 hens, using the roughly 1-box-per-3-4-hens ratio; more boxes than that generally go unused since hens tend to favor a couple of preferred spots.
Can I use chicken wire for the run?
Standard chicken wire keeps chickens contained but doesn't reliably keep predators out; hardware cloth (welded wire mesh, typically 1/2 inch openings) is the safer 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 do not need supplemental heat and tolerate temperatures well below freezing as long as the coop is 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.