Carpentry Calculators

Chicken coop size calculator

Enter how many birds and how big they are. This works out the coop floor, the run, the roost, the nest boxes and the ventilation from university extension figures you can change, then a coop of whole feet that holds them.

5 ft4 ft6 birdsrun10 ft
Breed size
Per-bird figures3 sq ft floor · 8 sq ft run · 9" roost · a box per 4 · 4 ft deep

Defaults from Colorado State University Extension (floor, run and roost, by breed size) and Oregon State University Extension (nest boxes). Change any of them to your own extension office's figures.

sq ft

Per bird

sq ft

Per bird

in

Per bird

sq ft

Rule of thumb, not an extension figure

ft

Front to back

Coop floor

18sq ft

Build

5 × 4 ft

Run

48 sq ft

Nest boxes

2

Roost

54"

Name this job

Saved jobs stay in this browser. Nothing is sent anywhere, and a save is not a backup — a link is how you move one to another device.

For 6 birds

Coop floor3 sq ft a bird
18 sq ft
Run8 sq ft a bird, outdoors
48 sq ft
Roost bar9" a bird, poles 10" apart
54"
Nest boxesOne per 4 birds, 12" × 12" × 12"
2
Ventilation1 sq ft per 10 sq ft of the coop as built — high on the walls, above the roosts
2 sq ft

A coop that holds them

Coop20 sq ft — whole feet, rounded up from 18 sq ft
5 × 4 ft
Run alongside50 sq ft along the coop's long side
5 × 10 ft
Roost barsThe length of the coop, higher than the nest boxes
1 × 5 ft
All 2 checks passShow the numbers
  • Roost bars fit 10" apart across the coop — passes1 bar the length of the coop take 10" of its 48" depth.
  • Nest boxes fit in one row along the coop — passes2 boxes 12" wide take 24" of a 60" wall.

Where these numbers come from

Floor, run and roost are Colorado State University Extension's ranges (Boulder County, “Backyard and Small Flock Poultry”), read low, middle and high for bantam, standard and large birds. One nest box per four birds, 12" boxes and roost poles 10" apart are Oregon State University Extension's (EC 1644). Neither gives a ventilation area — Oregon State asks for as much as you can manage without a draft — so that figure is the common rule of thumb and is yours to change. Birds kept in with no run need far more floor: Oregon State says 8 to 10 sq ft each. Check your town's rules on flock size and setbacks too.

Where to buy this

Or build them: a 12-inch cube with a sloped top is Oregon State's whole specification.

Plain search links, nothing sponsored. Prices and stock are the shop's, and a local lumberyard will usually beat both on solid stock.

Worked example: 6 standard hens

6 standard hens at 3 sq ft each need 18 sq ft of coop floor, 48 sq ft of run, 54" of roost and 2 nest boxes — Colorado State and Oregon State Extension figures, every one editable.

A 4 ft deep coop rounds up to 5 × 4 ft (20 sq ft), with 2 sq ft of ventilation at 1 sq ft per 10 sq ft of floor and a 5 × 10 ft run alongside.

It passes all 2 of the layout checks the calculator applies.

Coop floor
18 sq ft
Coop to build
5 × 4 ft
Run
48 sq ft
Roost
54"
Nest boxes
2
Ventilation
2 sq ft

These are the figures the calculator above opens on. Change any field and it works the same problem for your numbers.

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About chicken coop sizes

How big a coop do I need for 6 chickens?
About 18 sq ft of coop floor for six standard hens at 3 sq ft each — Colorado State Extension's middle figure — which a 4' deep coop rounds up to 5 × 4 ft. Add a run of 48 sq ft at 8 sq ft a bird, 2 nest boxes and 54" of roost. Those figures assume the birds get outside every day; Oregon State Extension asks for 8 to 10 sq ft each indoors if they do not.
How much roost space does a chicken need?
Colorado State Extension says 6" to 12" of roost per bird by breed size, and the calculator reads that as 6" for bantams, 9" for standard breeds and 12" for large ones. Oregon State's guide puts the poles about 2 ft off the floor and 10" apart, higher than the nest boxes so the birds sleep on the roost rather than in a box.
How many nest boxes do I need?
One for about every 4 hens, which is Oregon State Extension's figure (Colorado State says three to four). That is 2 for six hens and 3 for ten. Hens share, and usually all want the same one anyway; a 12" cube with a sloped top so nobody roosts on it is the whole specification.
How much ventilation does a chicken coop need?
The extension guides do not give a number. Oregon State asks for as much ventilation as you can manage without a draft on the birds — openings high on the walls, above the roosts, screened with hardware cloth. The calculator's default, one square foot of vent for every 10 square feet of floor, is the rule of thumb most coop plans repeat, and it is an input because a hot or damp climate wants more.

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