Coop and run sizing is one of the most common mistakes new backyard chicken keepers make — too little space leads to stress, pecking, and poor egg production. This calculator applies the standard backyard-poultry space guidelines cited by extension services and hatchery guides to your specific flock size, breed, and setup.
How the Chicken Coop Size Calculator works
The calculator multiplies your flock size by a fixed per-hen space allowance: 4 sq ft of coop floor space per standard hen, or 2 sq ft per bantam (bantams are roughly half the size of standard breeds). If you provide an outdoor run, it adds 10 sq ft per hen for the run — a larger allowance than the coop, since hens spend most of their active daytime hours there. Nesting boxes are calculated at one box per 4 hens (rounded up), and roosting bar length at 10 inches per hen.
Inputs and what they mean
Flock size is the number of hens you're housing — every output scales directly with this number.
Breed size (Standard vs Bantam) changes the coop space multiplier, since bantams are noticeably smaller birds and need less floor space, though they're just as active outdoors so run space stays the same.
Outdoor run toggles whether run square footage is included. Flocks without a run should plan for meaningfully more coop space than the bare minimum, since the coop is the only space the hens have to move around in.
Limits and edge cases
These are minimum space guidelines for healthy, low-stress flocks — more space is always better, and cramped conditions increase the risk of feather-pecking, bullying, and stress-related egg-production drops. Climate matters too: flocks in hot climates or those confined during bad weather benefit from extra coop space beyond the calculated minimum. This calculator doesn't account for mixed breed sizes within one flock — if you keep both standard and bantam hens, size the coop using the standard-hen rate for the whole flock to stay safely above the minimum.