Back garden hen housing planner

Chicken Coop Space Calculator

Plan indoor coop floor area, perch length, nest boxes and headroom for laying hens, with breed-size allowances and a check against the coop you have.

Enter Your Flock And Coop

Flock size Number of hens Use adult birds expected to sleep in this coop. hens Breed size Large breeds need more floor and perch room than bantams.

Coop to check Inside length Measure usable floor, excluding nest boxes if they take floor space. m Inside width Use the clear width available to the birds at night. m Usable perch length already fitted Total length of raised perch that birds can use at the same time. m

Housing features Nest box sharing ratio Four hens per nest box is a common planning allowance for small flocks. hens/box Clearance and cleaning allowance Add space for feeder, drinker, pop-hole queue, bedding depth and cleaning access. % Planned future hens Optional extra birds so the coop is not full on day one. hens

Coop Space Result

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Enter flock size and coop dimensions to see the result.

Fit check

This is a planning guide. More space, good ventilation, dry bedding and safe outdoor access matter as much as a floor-area number.

What Counts As Coop Space?

Coop space is the indoor, sheltered area where hens roost, shelter and lay. It is not the same as the outdoor run. A good coop needs enough usable floor area, enough perch length for all hens to settle at night, quiet nest boxes, dry bedding, ventilation without draughts, access for cleaning and a secure pop-hole. A coop can look large from the outside but still be tight inside if nest boxes, feeders, low roofs or steep ramps take up the usable area.

This calculator gives a practical small-flock planning figure rather than a legal stocking-density decision. DEFRA’s code for laying hens and pullets explains welfare duties and notes that commercial rules are recommended as good practice for smaller flocks. RSPCA advice also stresses room to roost, nest, forage and move without injury. For back garden keepers, the safer answer is nearly always to choose more space than the minimum, especially if birds will be shut indoors during bad weather or avian influenza housing measures.

How The Calculator Sizes A Coop

The tool starts with adult hens expected to sleep in the coop, then adds any future hens you are planning for. Breed size changes the floor and perch allowance. Bantams take less room, while large breeds need wider perches and more floor space. The cleaning allowance adds practical space for bedding, droppings boards, feeder movement, drinker access and people reaching inside. That allowance is not a welfare luxury; it is the gap between a theoretical box and a coop you can maintain without crowding birds.

The result also checks the coop you have entered. A floor-area pass does not mean the design is good. Perches need safe height and landing room. Nest boxes should be quiet and accessible. Ventilation should remove moisture and ammonia without chilling the birds at roost. A secure coop also needs predator-resistant latches, sound mesh, a dry roof and regular red-mite checks.

Formula And Method

Planning hens = current hens + future hens Required floor area = hens x breed floor allowance x (1 + cleaning allowance) Required perch length = hens x breed perch allowance Nest boxes = hens divided by nest-box sharing ratio, rounded up

The default standard-hen allowance is a practical backyard planning value, not a statement of a single legal minimum. It is intentionally paired with perch and nest calculations because floor area alone misses common coop problems. The calculator rounds nest boxes up to whole boxes and perch length to centimetres. For mixed flocks, choose the larger breed size or run separate checks for each group.

Worked Coop Examples

Six hybrid hens

Six standard hens need enough floor area for roosting and movement plus about 1.2 m of perch at 20 cm each. If the coop has only 90 cm of usable perch, birds may sleep in nest boxes or bully lower-ranking hens off the roost.

Three bantams

Bantams usually need less space per bird, but they still need dry bedding, safe perches and predator protection. A tiny decorative coop can fail because it is hard to clean or poorly ventilated, even if the floor number looks acceptable.

Large breed flock

Eight large hens need more width, stronger perches and easier access. A perch designed for light hybrids may bend or force heavy birds to land awkwardly, raising injury risk.

Coop Feature Checklist

Feature	What to check	Why it matters
Perch space	Enough raised perch for all hens at once, with safe landing space.	RSPCA guidance refers to roosting space from 15 cm per chicken; many backyard keepers use more for comfort.
Nest boxes	Quiet, darker boxes with clean bedding and easy egg collection.	Too few boxes can lead to floor eggs, queueing or dirty eggs.
Ventilation	High-level vents that remove damp air without a draught at perch height.	Moisture and ammonia can harm welfare and make bedding wet.
Cleaning access	Large door, removable tray, smooth surfaces and room to reach corners.	A coop that is hard to clean is more likely to harbour red mite and damp bedding.
Predator security	Sound mesh, lockable pop-hole, no gaps and strong base edges.	Foxes, rats and other predators exploit small gaps and weak latches.

Coop Space Is Not Run Space

The coop is only the indoor sleeping and laying area. Hens also need outdoor space or a secure run for foraging, dust bathing and daytime movement. A flock with a generous run may still need a well-sized coop because all birds return to the enclosed house at night. During disease-control housing orders, birds may spend much more time under cover, so extra indoor and covered-run space becomes more important.

When A Bigger Coop Is The Better Answer

Choose a larger coop if you are new to keeping hens, if the flock includes large breeds, if children will help with care, if the coop will stand in a damp area, or if you expect to add birds later. Extra space also makes it easier to isolate a bullied hen, fit feeders without blocking movement and clean without dismantling the whole house. The purchase cost can be higher, but cramped housing often costs more in stress, injuries, dirty eggs and maintenance.

FAQs

How much coop space does a chicken need?

There is no single perfect number for every backyard coop. Use a floor allowance, perch length, nest boxes and cleaning space together. More space is safer than packing birds tightly.

Can nest boxes count as floor area?

Usually they should be treated separately, especially if they are raised or enclosed. Hens use nest boxes for laying, not as general movement space.

How many nest boxes do I need?

For small flocks, one box per three or four hens is a common planning rule. Some hens will still queue for the same favourite box, so having at least two boxes can help.

How much perch space should I allow?

RSPCA advice mentions enough space for all chickens to roost at the same time, from 15 cm per chicken. Many backyard coops use around 20 cm for standard hens and more for large breeds.

Can this replace welfare or veterinary advice?

No. It is a sizing planner. Use official welfare guidance, product measurements and veterinary advice for health, injury or behaviour problems.

Sources

Department for Environment, Food and Rural Affairs. (2023). Code of practice for the welfare of laying hens and pullets. GOV.UK. https://www.gov.uk/government/publications/poultry-on-farm-welfare/poultry-welfare-recommendations
RSPCA. (2026). Tips for housing and outdoor space for pet chickens. https://www.rspca.org.uk/adviceandwelfare/farm/farmanimals/chickens/environment
RSPCA. (2025). RSPCA welfare standards for laying hens. https://www.rspca.org.uk/documents/d/rspca/rspca-welfare-standards-for-laying-hens