4 sq ft inside. 10 sq ft of run. Per bird. That's the fight on every chicken forum.

Extension-service numbers, rounded up. Not the 2 sq ft prefab that looks cute on Amazon until week six.

Roost bar: Utah lists 6 to 10 inches per bird. Nesting boxes: one per 4 to 5 hens, and they will still queue for the same box. The housing pages cited here do not set an adult heat-lamp cutoff. Damp air is the winter problem they describe.

Use it in 10 minutes. Count standard birds. Multiply by 4 sq ft inside and 10 sq ft of run. Bantam minimums on the Penn State and Maryland tables are 1 sq ft inside and 4 sq ft of run. This card's calculator link uses 2 and 8, which is extra room above that minimum.

Quick reference by flock size (standard birds)

Flock	Coop sq ft	Run sq ft	Nest boxes	Feed / month
3 hens	12	30	1	23 lb (~1 bag / 2 mo)
6 hens	24	60	2	46 lb (~1 bag / mo)
12 hens	48	120	3–4	91 lb (~2 bags)
25 hens	100	250	7–9	190 lb (~4 bags)

¼ lb layer feed per day (Alabama and Kentucky Extension). $22 per 50 lb bag is the calculator default, not a published price. Nest counts in the table are this card's tighter one-per-3 planning count; published guidance is one per 4 to 5 hens.

Every flock count this site covers, including the indoor minimum and the feeder rule past 25 birds, is on chicken coop size by flock size.

Worked 6-hen build: 4×6 coop, ~6×10 run, 5 ft of roost, two boxes, one 50 lb bag a month. Heat lamp is for chicks in a brooder, not a dry adult flock.

Comment keyword: HENS — that's the word we ask for on X/LinkedIn. We DM this page.

Size your flock → Print / Save PDF

Sources & Standards

Published references for coop space, nests, and feed:

Frequently asked questions

Is this calculator free?

Yes — free to use, no signup, no email required.

How accurate is the estimate?

Estimates follow industry-standard sizing rules and common safety margins. Always confirm with a licensed professional for final sizing.

Can I use this on mobile?

Yes — the page is fully responsive and works on phones, tablets, and desktop.

Where does the math come from?

Formulas are shown inline on the result panel so you can verify each step yourself.