Chicken coop size calculator
Most coop calculators multiply your hens by four and stop there. Whether your birds free-range, how big they are and how cold your winters get all change the answer — so this one asks.
Build a 4′ × 6′ coop
- Coop floor
- 24 ft²
- Suggested size
- 4′ × 6′
- Run
- 60 ft²
- 4′ × 15′
- Roost bar
- 60″ total
- Nesting boxes
- 2
- 12″ square each
- Ventilation
- 2.4 ft²
- permanent, up high
- Bedding
- 8 ft³
- ≈ 1 bags of shavings
Build bigger than the number. Nearly every keeper adds birds within two years, and expanding a finished coop costs far more than adding two feet at the framing stage.
Why "4 square feet per hen" is only half the rule
The familiar figure assumes birds that have somewhere to go during the day. A flock locked in the coop full time needs roughly double the interior space — closer to 8 ft² per standard hen — because the coop is no longer just a place to sleep and lay. Birds that free-range from dawn to dusk can manage on less, since they are only inside to roost.
Breed size shifts it again. Bantams do fine at 2 ft², standard breeds want 4, and heavy birds like Jersey Giants and Brahmas need 6. Mixing sizes? Size for the biggest.
Overcrowding doesn't look like overcrowding
This is the part worth getting right, because a cramped coop announces itself as behavioural problems rather than a space problem. Feather picking, hens that will not go in at night, bullying of the bottom bird, a sudden drop in laying, and outbreaks that spread through the whole flock — all of these get blamed on feed, mites or the weather far more often than on square footage.
Once picking starts it is a hard habit to break. Building 20% larger than the number above is the cheapest insurance in the whole project.
Ventilation: the thing that kills birds in winter
Chickens wear a down coat and handle cold far better than people expect. What they do not handle is moisture. A flock breathing and dropping manure in a sealed coop drives humidity up all night, and damp air at freezing temperatures causes frostbitten combs and respiratory disease. Cold and dry is fine; cold and damp is dangerous.
The baseline is about 1 ft² of permanent, year-round vent per 10 ft² of floor — and cold climates need more, not less, which is exactly backwards from most people's instinct to seal everything up for winter. Put vents high, above roost height, so warm moist air escapes without blowing directly on the birds. Hot climates need roughly double for airflow: heat stress kills more birds than cold does.
Roosts, nesting boxes and bedding
- Roost: 10 inches per standard hen, plus a couple more each in cold climates where they press together for warmth. Use a 2×4 laid flat so they can cover their feet — round bars leave toes exposed to frostbite.
- Nesting boxes: one per four hens, about 12 inches square. Adding extras rarely helps; they will queue for whichever box is fashionable that week.
- Bedding: 4 inches is standard. Going to 6 or more sets you up for the deep litter method, where the bedding composts in place over winter and generates a little heat — but it only works with the ventilation above, otherwise you are building a damp box.
Before you cut lumber
The suggested dimensions use even-foot widths so sheet goods and standard lumber cut with minimum waste. Two things the calculator can't tell you: check your local ordinance for coop setbacks from property lines, and plan the door before the walls — a coop you can walk into is dramatically easier to clean than one you have to crawl into, and you will be cleaning it for years.
Not sure how many hens you need in the first place? Start with the flock size calculator and come back — this page will offer to pull that number in.