Quick Answer: For standard-size hens, multiply your flock count by 3-4 sq ft of coop floor and 8-10 sq ft of run space per bird — a flock of 6 needs roughly 18-24 sq ft of coop and 48-60 sq ft of run, according to the extension-guideline numbers used sitewide. Bantams need about a third less (2-3 sq ft coop / 6-8 sq ft run per bird); large dual-purpose breeds like Brahmas need the top of the standard range. The tables below do this calculation for flock sizes from 2 to 20 birds so you don’t have to.
Most “chicken coop size calculator” searches expect an interactive tool, but the honest version of this calculation is simple enough that a lookup table is faster than a form with dropdowns — the underlying math is just flock count times a per-bird multiplier, and the multiplier only changes with breed size. This guide gives you both: the exact numbers for common flock sizes, and the formula if your count falls outside the table.
Coop size by flock size (standard breeds)
| Flock size | Coop floor (3-4 sq ft/hen) | Run space (8-10 sq ft/hen) | Total footprint |
|---|---|---|---|
| 2 hens | 6-8 sq ft | 16-20 sq ft | 22-28 sq ft |
| 4 hens | 12-16 sq ft | 32-40 sq ft | 44-56 sq ft |
| 6 hens | 18-24 sq ft | 48-60 sq ft | 66-84 sq ft |
| 8 hens | 24-32 sq ft | 64-80 sq ft | 88-112 sq ft |
| 10 hens | 30-40 sq ft | 80-100 sq ft | 110-140 sq ft |
| 12 hens | 36-48 sq ft | 96-120 sq ft | 132-168 sq ft |
| 15 hens | 45-60 sq ft | 120-150 sq ft | 165-210 sq ft |
| 20 hens | 60-80 sq ft | 160-200 sq ft | 220-280 sq ft |
These figures assume the run is the flock’s only outdoor access, with no regular supervised free-range time — the standard planning assumption, since most keepers can’t guarantee daily free-range and it’s safer to size for the worst case. If your flock free-ranges most days, you can lean toward the lower end of the run-space range; a coop that’s rarely used except at night has more flexibility on square footage than one the flock lives in full-time.
Coop & Run Building Materials
- Once you know the target square footage, our chicken coop plans guide breaks it down into buildable dimensions rather than just a total number.
- Whatever footprint you land on, wrap it in ½-inch hardware cloth, not chicken wire — chicken wire stops chickens from leaving, not predators from getting in.
- Sizing a run from scratch? Our chicken run ideas guide covers 15 layouts, from $280 cattle-panel hoops to modular expandable kits, at whatever footprint the table above gives you.
Sourcing plans, hardware cloth, and fasteners from a reading list before you start cutting wood beats improvising mid-build. Try Kindle Unlimited free for a stack of backyard-coop building and flock-keeping field guides while you plan the cut list.
Coop size by flock size (bantam breeds)
Bantams run about a third smaller than standard breeds, so the per-bird multiplier drops to roughly 2-3 sq ft of coop and 6-8 sq ft of run.
| Flock size | Coop floor (2-3 sq ft/hen) | Run space (6-8 sq ft/hen) | Total footprint |
|---|---|---|---|
| 4 bantams | 8-12 sq ft | 24-32 sq ft | 32-44 sq ft |
| 6 bantams | 12-18 sq ft | 36-48 sq ft | 48-66 sq ft |
| 8 bantams | 16-24 sq ft | 48-64 sq ft | 64-88 sq ft |
| 10 bantams | 20-30 sq ft | 60-80 sq ft | 80-110 sq ft |
Don’t mix the bantam multiplier into a flock that also has standard-size birds — calculate each group separately at its own per-bird number and add the totals, since a Brahma and a Silkie need genuinely different floor space even standing side by side.
Coop size for large & dual-purpose breeds
Large-bodied dual-purpose breeds — Brahmas, Jersey Giants, Orpingtons — do better at the top of the standard range rather than the midpoint, since they’re meaningfully bigger-bodied than a Leghorn or Easter Egger at the same “standard hen” label.
| Flock size | Coop floor (4 sq ft/hen) | Run space (10 sq ft/hen) |
|---|---|---|
| 4 hens | 16 sq ft | 40 sq ft |
| 6 hens | 24 sq ft | 60 sq ft |
| 8 hens | 32 sq ft | 80 sq ft |
If you’re not sure whether a breed counts as “large,” check its adult weight — anything over roughly 8-9 lbs for a hen (Brahma, Jersey Giant, Cochin) is worth sizing at the top of the range rather than the standard 3-4 sq ft minimum.
The formula, if your flock falls outside the tables
Coop floor space = number of hens × 3-4 sq ft (2-3 for bantams, 4 for large breeds) Run space = number of hens × 8-10 sq ft (6-8 for bantams, 10 for large breeds)
This is floor space only — before counting roost bars or nesting boxes, and before any winter-specific reduction in outdoor time. For the reasoning behind these multipliers, including what happens when a flock is overcrowded below them, see our full how much space do chickens need guide.
The bottom line
The math behind chicken coop sizing is simple enough that you don’t need a live calculator tool — flock count times 3-4 sq ft of coop and 8-10 sq ft of run per standard hen covers the large majority of backyard setups, with bantams running about a third smaller and large dual-purpose breeds sizing at the top of that range. Round up rather than down if your count falls between rows, since flocks tend to grow. Once you have a target footprint, our chicken coop plans and chicken run ideas guides turn that number into an actual buildable layout.