What Size Coop for 20 Chickens?
20 standard hens need 80 sq ft of coop floor and 200 sq ft of run, plus 5 nest boxes and 16 ft 8 in of roost. Adjusted for breed, climate and setup.
20 standard-size hens with access to a run need 80 square feet of coop floor and 200 square feet of run, plus 5 nest boxes and 16 ft 8 in of roost bar. Confined without a run, the coop figure rises to 200 sq ft. In a cold climate add about 25%, giving 100 sq ft. Heavy breeds need 100 sq ft; bantams 40.
Change the breed, climate or setup and see the numbers move with the coop size calculator.
What size coop for 20 chickens?
For 20 standard-size hens — Plymouth Rocks, Orpingtons, Rhode Island Reds — that spend their days in a run:
| What | How much | Why |
|---|---|---|
| Coop floor | 80 sq ft | 4 sq ft per bird, sleeping and laying space |
| Run | 200 sq ft | 10 sq ft per bird of enclosed outdoor space |
| Nest boxes | 5 | Two minimum, then about one per four hens |
| Roost bar | 16 ft 8 in | 10 inches per bird, splittable across bars |
| Ventilation | 2,880 sq in | High-mounted, to clear moisture and ammonia |
A 8×10 footprint gives 80 sq ft, which covers it. The run wants 200 sq ft alongside it.
If the setup is different
The coop figure assumes the birds get outside every day. Change that and it moves:
| Setup | Coop floor | Run |
|---|---|---|
| With a run (the usual case) | 80 sq ft | 200 sq ft |
| Confined, no run | 200 sq ft | — |
| Free-ranging most of the day | 60 sq ft | 200 sq ft or open ground |
Confining birds without a run roughly doubles what the coop has to provide, because it stops being a bedroom and becomes the whole living space.
By breed
Body size moves the figure more than most people expect:
| Breed tier | Examples | Coop | Run | Roost |
|---|---|---|---|---|
| Heavy | Brahma, Jersey Giant, Cochin | 100 sq ft | 240 sq ft | 16 ft 8 in |
| Standard | Plymouth Rock, Orpington, Rhode Island Red | 80 sq ft | 200 sq ft | 16 ft 8 in |
| Light | Leghorn, Hamburg, Andalusian | 60 sq ft | 160 sq ft | 16 ft 8 in |
| Bantam | Silkie, Sebright | 40 sq ft | 120 sq ft | 6 ft 8 in |
A mixed flock takes the larger figure. 20 birds that include heavy breeds should be sized as 20 heavy birds — the big ones do not confine themselves to their share.
Cold climates
In a cold climate, add about 25% to the indoor figure: 100 sq ft for 20 standard hens rather than 80.
Not because chickens need more room when cold — they huddle for warmth — but because a cold-climate flock spends far more days shut in, and the moisture from droppings and breathing has to go somewhere. Winter coop trouble is usually a crowding and ventilation problem wearing a temperature costume. The 25% figure is a Flockmath planning convention rather than a published minimum; the direction is supported, the number is ours.
Walk-in is worth it at this size
80 sq ft works on paper as a low structure, but past about a dozen birds the real constraint is access rather than floor area. If you cannot stand up inside, you will not clean it properly, and a coop that does not get cleaned develops an ammonia problem regardless of its square footage.
A walk-in build with full headroom costs more up front and pays it back in the years you actually keep using it. The 200 sq ft run is usually the harder constraint in a suburban yard — that is a footprint around 10×20, which is more ground than most people picture when they plan for 20 birds.
Check local zoning too. Many municipalities cap backyard flocks below 20.
Frequently asked questions
How big should a chicken coop be for 20 chickens?
80 square feet of floor for 20 standard-size hens with a run, plus a 200 square foot run. Confined without a run, 200 square feet.
How many nest boxes for 20 chickens?
- The rule is two minimum, then roughly one per four hens. Extra boxes past that are mostly wasted — hens cluster on one or two favourites regardless.
How much roost space for 20 chickens?
16 ft 8 in of bar, at 10 inches per standard bird. Several bars at different heights work fine; the dominant birds take the highest.
Does the run have to be 200 square feet?
That is the working minimum at 10 sq ft per standard bird. A run at the minimum will go to bare earth, which is normal rather than a failure. Keeping ground vegetated takes far more space — see how many square feet per chicken.
Sources
- Poultry Extension — space allowances for small and backyard flocks: 3 to 4 square feet of indoor space per hen plus about 10 square feet outdoors.
- Penn State Extension — small-scale poultry housing: outdoor minimums by bird type, which every run figure here meets or exceeds, and two nests for the first four hens.
- Virginia Cooperative Extension — small-scale poultry housing: roost length, published as 8 to 10 inches per bird.
Every figure on this page is produced by the same engine as the coop size calculator, where the sourcing for each is set out in full — including which are Flockmath planning conventions rather than published minimums. The 25% cold-climate adjustment and the ventilation figure are ours; the floor, run, nest-box and roost figures come from the extension sources above.
Figures are welfare minimums and planning guidance, not veterinary advice. Local zoning may cap flock size. Last reviewed August 2026.