Say how many birds you have and how they live, and you get the coop floor, the run, the nest boxes, the roost length and a footprint you could actually build — worked out three times, because the three extension services that publish these numbers do not agree. One says 1.5 square feet a hen indoors; another says 3.
6 birds
9–24 sq ft of coop
Coop floor — what each source says
Run
Inside the coop
More space is never the problem; too little is. A crowded flock in a long winter is where feather-pecking and bullying start, and no amount of arithmetic fixes it afterwards.
Space guidelines checked 2026-09-22.
Quick answer: for six standard hens with a run, the published minimums give you anywhere from 9 to 24 square feet of coop — Penn State says 1.5 sq ft a hen, Oregon State says at least 3, poultry.extension.org says 3 to 4 — plus 48 to 60 square feet of run, 2 or 3 nest boxes and 36 inches of roosting bar (Penn State) or 30 to 60 (Oregon State). Birds with no outdoor space at all need much more: Oregon State’s figure is 8 to 10 square feet each.
Why you get three answers
Every chicken coop calculator online prints one number. There are three, they come from three extension services, and they differ by a factor of two:
- Penn State Extension — 1.5 sq ft indoors per standard hen, 1 for a bantam, 2 for a large bird; 8 sq ft of run per standard hen, 4 for a bantam.
- Oregon State Extension — at least 3 sq ft per bird with access to a run, and 8 to 10 sq ft per bird with no outdoor access.
- poultry.extension.org — 3 to 4 sq ft indoors per hen and 10 sq ft outdoors.
None of them is wrong. Penn State’s is the minimum a bird can be kept in; the others are what a flock is comfortable in. An average of the three would be a number nobody published, so this calculator shows all three and lets you decide which end of that range you are building to. If you are asking the question at all, build toward the generous end — the cost of extra space is plywood, and the cost of too little is feather-pecking in February.
Nest boxes: two rules, both simple
Penn State says two nests for the first four hens and one more for every four after that. Oregon State says one for about every four birds. Either way, a box about 12 inches square, off the ground but lower than the roosts — hens want to sleep on the highest thing in the coop, and if that is the nest boxes they will sleep in them and foul the eggs.
Roosting bars
Penn State: 6 inches of bar per standard bird, 4 per bantam, set 18 to 24 inches off the floor (12 to 18 for bantams). Oregon State: 5 to 10 inches per bird, bars 2 feet up and 10 inches apart, made from 1- to 2-inch lumber with the top edges rounded off — a bar that is too thin or too round causes foot problems. Silkies are the exception everybody forgets: they cannot fly up, so their bar goes about a foot off the ground.
Ventilation — the number nobody publishes
You will see “one square foot of vent per bird” quoted all over the internet. I could not find it in any extension publication, so this calculator does not print it. What Oregon State does say is the useful part: build in as much ventilation as you can without creating a draught, and keep it up high, above the birds’ heads when they are on the roost. Moisture, not cold, is what gives chickens frostbitten combs — a sealed coop in January is worse than a breezy one.
Predator-proofing, while you are building
Oregon State’s list is worth following while the coop is still a pile of timber: raise it at least a foot off the ground, use 1-by-2-inch mesh rather than chicken wire, put netting or wire over the top of the run, and bury the fencing 6 inches to a foot deep against anything that digs. A door that shuts the flock in at night is the single most effective part of it.