Coop space per bird
As a baseline, standard-size breeds need at least 3-4 square feet of enclosed coop floor space per bird with outdoor run access, and closer to 8-10 square feet per bird if they'll be coop-confined most of the time — cold climates with limited winter outdoor access, for instance. Bantam breeds need roughly half that. Size for your maximum expected flock, not your starting flock — 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 room than the coop itself: plan at least 8-10 square feet per bird, and 15+ square feet per bird if the flock won't be free-ranging elsewhere during the day. Birds confined to an undersized run show far more pecking-order aggression and feather picking. If space is tight, vertical elements like perches and platforms help birds use the run more efficiently.
How many nesting boxes you actually need
One nesting box per 3-4 hens is sufficient — hens share readily and often favor the same one or two 'popular' boxes even when others sit open. Standard box dimensions run roughly 12x12x12 inches for standard breeds, positioned lower than the roosting bars so birds don't try to sleep in them (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 — a 2x4 laid flat, for example — rather than a round dowel, since flat bars let birds cover their feet with their bodies for warmth in cold weather. Roosts should sit higher than nesting boxes, since chickens instinctively seek the highest available sleeping 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 tight for winter is a common and serious mistake. For predator-proofing, use hardware cloth (not chicken wire, which larger predators tear through) on every opening, bury or apron the run's perimeter fencing at least 12 inches to stop digging predators, and secure a locking mechanism predators can't work — 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 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, using the roughly 1-box-per-3-4-hens ratio. More than that typically goes unused since hens 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 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.