Chicken Coop Size Calculator
Size a backyard chicken coop and run from your flock size, breed (or a mixed flock with bantams) and whether birds free-range or stay in — with suggested dimensions, nesting boxes, roost length, ventilation, daily feed and water, and a check of how many birds an existing coop and run can hold.
How it works
Coop = birds × coop sq ft/bird (with a run or free-ranging: bantam 1, standard 3, large 4; generous 2/4/6; kept inside: 4/10/12) · Run = birds × run sq ft/bird (enclosed: 4/8/10, generous 8/15/20; free-range shelter: 1/2/2.5) · Nesting boxes = ⌈hens ÷ hens per box⌉ · Roost = birds × 6/10/12 in · Ventilation ≈ coop floor ÷ 10 · Feed ≈ 0.15/0.25/0.3 lb per bird per day
Crowding is a leading cause of stress, feather-pecking and disease in backyard flocks, so housing is planned per bird. Inside the coop, standard laying hens with access to a run need about 3–4 square feet each, bantams 1–2 and large or heavy breeds 4–6; birds that are kept inside all the time need much more — around 10 square feet per standard hen — because the coop is their whole world. The run needs far more room than the coop, roughly 8–10 square feet per standard bird and 15 or more for a generous setup, because that is where chickens forage, dust-bathe and burn energy; birds that free-range by day need only a smaller covered shelter. A mixed flock adds the bantams at bantam rates. Nesting boxes follow their own rule — one box for every three to five hens, roosters excluded — and roost bars need about 10 inches per standard bird so the flock can sleep side by side. A common ventilation rule is one square foot of openings, high up and away from roosting birds, for every ten square feet of floor. Enter the size of an existing coop or run to see how many birds it holds.
Worked example
Six standard hens in a coop-plus-run setup need 6 × 3 = 18 sq ft of coop (for example 3 × 6 ft) and 6 × 8 = 48 sq ft of run (6 × 8 ft), about 66 sq ft in all. With one box per four hens they need 2 nesting boxes, 60 inches (5 ft) of roost, about 1.8 sq ft of ventilation, and roughly 1.5 lb of feed and 0.75 gallon of water a day. An existing 4 × 4 ft coop (16 sq ft) is 2 sq ft short and holds 5 standard hens.
Sources: Omni Calculator — Chicken Coop Size Calculator (coop space by daytime setup) · The Happy Chicken Coop — How much room do chickens need?
Frequently asked questions
How much space does a chicken need?
Plan about 3–4 square feet of coop plus 8–10 square feet of run per standard-size hen. Bantams need less (roughly 1–2 sq ft of coop), and large or heavy breeds more. Birds that free-range by day can manage with a smaller covered shelter for nights and bad weather, while birds kept inside all the time need around 10 sq ft each.
How many nesting boxes do I need?
One nesting box for every three to four hens is the usual guideline, and up to five hens can share a box. Roosters do not use them. Hens often queue for the same favourite box, so more boxes than that usually go unused — but too few leads to squabbling and eggs laid on the floor.
How long should the roost bar be?
Allow about 10 inches per standard hen, 6 inches per bantam and 12 inches per large breed. Birds huddle in winter and spread out in summer, so err on the generous side, and put roosts higher than the nesting boxes so hens do not sleep in them.
How many chickens fit in a 4 × 8 coop?
A 4 × 8 ft coop is 32 sq ft: about 10 standard hens with an outdoor run (3 sq ft each), 8 at a generous 4 sq ft, or only 3 if they never go outside. Enter the coop’s length and width under “More options” to check any size.
Is more space always better?
Generally yes for outdoor run space, which reduces boredom, pecking and disease pressure. The main limits are predator-proofing a larger area and keeping the coop warm in cold climates, where an over-large coop can be harder for the flock to heat with their own body warmth.
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General guidance — consult your vet for your specific animal.