Calculate the minimum coop and run size for your flock in square feet or square meters, or find how many chickens fit a coop you already have.
Chicken Coop Size Formula
The calculator works in two directions. To size a coop and run for a known flock, it multiplies the number of birds by the space each bird needs:
Coop = N * A Run = N * R
To find how many birds an existing coop holds, it divides the coop floor area by the space per bird and rounds down:
Max Birds = floor(Coop Area / A)
Variables:
- Coop is the minimum coop floor area
- Run is the minimum outdoor run area
- N is the number of birds
- A is the coop floor space per bird, which is 4 sq ft for a standard bird with run access, 10 sq ft if confined full-time, and 3 sq ft if free-ranging
- R is the run space per bird, about 10 sq ft for a standard bird and 5 sq ft for a bantam
- Max Birds is the largest comfortable flock for a coop of a given area
Pick what you want to find at the top of the calculator. In “Coop and run size for my flock” mode you enter how many standard chickens and bantams you keep, and the tool returns the coop area, run area, and the fittings that go inside. In “How many chickens fit my coop” mode you enter the coop area or its length and width, and the tool returns the maximum flock plus the run and fittings to match. The daytime setting changes A, since birds locked in all day need far more floor space than birds that only sleep inside.
The same result also sizes the parts inside the coop. Nesting boxes come from the number of hens, roost length from the number of birds, and ventilation from the finished floor area:
Boxes = roundup(Hens / 4) Roost = N * 8 in Vent = Coop Area / 10
You can raise the roost allowance to 10 or 12 inches per bird and tighten the box ratio to one per three hens in the advanced options.
Space Per Bird By Setup
The floor space a bird needs depends mostly on where it spends the day. These are the per-bird figures the calculator uses.
| Daytime setup | Coop per standard bird | Coop per bantam |
|---|---|---|
| In a fenced run | 4 sq ft | 2 sq ft |
| Confined full-time | 10 sq ft | 4 sq ft |
| Free-ranging the yard | 3 sq ft | 1 sq ft |
Breed size shifts these numbers. Most calculators use one flat figure, but a Jersey Giant does not fit the same space as a Leghorn. Use this guide to pick the coop figure that matches your birds, then enter it as extra area if your flock is on the heavy end.
| Breed class | Examples | Coop per bird (run access) | Run per bird |
|---|---|---|---|
| Bantam | Silkie, Sebright, Serama | 2 sq ft | 5 sq ft |
| Light | Leghorn, Ancona, Fayoumi | 3 sq ft | 8 sq ft |
| Standard dual-purpose | Rhode Island Red, Australorp, Sussex | 4 sq ft | 10 sq ft |
| Heavy or large | Orpington, Brahma, Jersey Giant | 6 sq ft | 15 sq ft |
Example Problems
Example 1: Size a coop and run for a flock.
You keep 6 standard hens that use a fenced run during the day. The coop needs 6 times 4 sq ft, which is 24 sq ft, so a 4 ft by 6 ft coop works. The run needs 6 times 10 sq ft, which is 60 sq ft. You round 6 hens up to 2 nesting boxes, and the roost bar needs 6 times 8 inches, which is 48 inches, or 4 feet.
Example 2: Find how many birds a coop holds.
You have a 4 ft by 4 ft coop, which is 16 sq ft, and your birds use a run. Divide 16 sq ft by 4 sq ft per bird to get 4 standard hens. That flock wants about 40 sq ft of run, one nesting box, and a 32 inch roost bar.
Frequently Asked Questions
How much space does one chicken need in a coop?
A standard chicken needs about 4 sq ft of coop floor when it has a run to use during the day. Raise that to 10 sq ft if the bird is shut inside full-time, and you can drop to 3 sq ft if it free-ranges the yard and only sleeps in the coop. Bantams need roughly half of each figure. These are minimums, and giving more space lowers pecking and keeps the litter cleaner.
How big should the run be?
Plan at least 10 sq ft of run per standard bird and about 5 sq ft per bantam. More is better here than anywhere else, because a roomy run cuts down on mud, boredom, and bullying. If you can give 20 sq ft or more per bird, behavior problems become rare.
How many chickens can I keep in a 4 by 8 coop?
A 4 ft by 8 ft coop is 32 sq ft. With a run for daytime use at 4 sq ft per bird, that holds 8 standard hens. If the birds stay inside full-time at 10 sq ft each, the same coop holds only 3. Switch the calculator to “How many chickens fit my coop” to run these numbers for any size you have in mind.
