I don’t believe in magic numbers for chickens. We keep them in so many different conditions, in different climates, with different flock make-ups, use so many different management techniques, and have different goals so no one magic number will cover us all. Summer in Miami may be different from winter in Nova Scotia, for example. I find that the tighter I crowd them the more behavioural problems I am likely to have, the less flexibility I have in dealing with problems, and the harder I have to work.
The behavioral problems from overcrowding could be anywhere from them being loud, feather-picking, bullying, fighting, all the way to cannibalism. Flexibility is not just dealing with behavioral problems but maybe integration and broody hens, predator problems or many other things. As an extreme example, say you have damage to your run where you cannot safely keep your chickens penned during the day. Do you have to miss a day’s work or not take your kids to school to deal with it immediately or can you lock them in the coop until you have time to deal with it on your schedule? As for hard work, think poop management. The smaller space they are in the more you have to physically manage the poop.
What is important is how much space is available when they need it. Whether that space in in your coop, coop and run, or they sleep in trees and totally free range doesn’t matter. If all you use your coop for is to provide a safe place for them to sleep and you commit to getting up when they do 365 days a year so you can open the pop door, you really don’t need much space in the coop itself. The space available is the coop plus the run or maybe free range. But the more you commit yourself to a specific way of managing them, the less flexibility you have. For instance, how hard will it be to find someone to take care of your chickens when you go on vacation if they have to be there at dawn as opposed to 9:00 a.m. being OK?
I understand that people without experience need general guidelines to go by. There are several rules of thumb to help people get started. A popular one on this forum is 4 square feet per chicken in the coop along with 10 square feet per chicken in the run. This is geared toward people with a small backyard flock in suburbia, not a big flock in a rural setting. It will keep most people out of trouble in a wide range of climates and using different management techniques. That means it is overkill for a lot of people as far as the bare absolute minimum they could get by with, but occasionally it proves to be a bit tight. Still it is a good starting point.
Some of the things that make up the space requirement are, in my opinion:
1. Personal space for the birds. They have different personalities and different individual requirements. Some are very possessive of personal space and some can share. Each flock has its own dynamics. There are breed tendencies but individual birds of the same breed can have totally different personalities.
2. Access to feeder and waterer.
3. Being able to put the feeder and waterer where they will not poop in it when they roost.
4. Roost spacing. They not only need to have enough room to sleep on the roost, they need to have enough room for them to spread their wings and fly to the roost and to sort out who gets to sleep next to whom and who gets the prime spots once they get on the roost. When they get on, they may jump from some midway support or fly directly to the roost, but either way, they like to spread their wings. And some chickens seem to enjoy blocking the entry points if there are limits. When they get off, mine tend to want to fly down, not jump to a halfway point. They need room to fly down without bumping into feeders, waterers, nesting boxes, or a wall.
The more chickens you have the less roost space per chicken you need. They don’t take up a lot of room when they are roosting once access and maneuvering room is provided. But I find that mine can be pretty vicious on the roosts as they are settling down, especially when I am integrating. I find it helps to have lots of roost space, not the bare minimum.
5. Poop load. The larger area they have the less often you have to actively manage the poop. They poop a lot while on the roost so you may have to give that area special consideration, but mucking out the entire coop can be backbreaking work plus you have to have some place to put all that bedding and poop. In my opinion, totally cleaning out the coop is something that needs to happen as seldom as possible.
You can help manage poop load by using a droppings board but that commits you to regularly scraping the poop off and dealing with it.
6. How often are they able to get out of the coop? How often they are allowed out of the coop may depend on a lot more than just weather. Your work schedule, when you are able to turn them loose, what time of day you open the pop door to let them out or lock them up at night, all this and more enters into the equation. The 4 square feet recommendation assumes they will spend extended time in the coop and not be able to get in the run occasionally. What that extended time can safely be depends on a lot of different factor so there is no one correct length of time for everyone.
7. Do you feed and water in the coop or outside. The more they are outside, the less pressure on the size of the coop.
8. The size of the chicken. Bantams require less room than full sized chickens. This has to be tempered by breed and the individual personalities. Some bantams can be more protective of personal space than others, but this is also true of full sized breeds. Young chicks need less space than mature adults but in a mixed age flock, extra room is important.
9. The breed of the chicken. Some handle confinement better than others.
10. The number of chickens. The greater the number of chickens, the more personal space they can have if the square foot per chicken stays constant. Let me explain. Assume each chicken occupies 1 square foot of space. If you have two chickens and 4 square feet per chicken, the two chickens occupy 2 square feet, which leaves 6 square feet for them to explore. If you have ten chickens with 4 square feet per chicken, each chicken has 30 unoccupied square feet to explore. A greater number also can give more space to position the feeders and waterers properly in relation to the roosts and provide access. In general the more chickens you have the less space per chicken you need.
11. What is your flock make-up? Adding one rooster to a flock of hens does not greatly increase the required space needed, though it sometimes helps flock dynamics if they have more space. But adding a second or additional roosters can greatly affect the amount of room they need. Often multiple roosters will split the flock into separate harems with each rooster claiming his own territory. That reduces conflict.
12. What is the maximum number of chickens you will have. Consider hatching chicks or bringing in replacements. Look down the road a bit.
13. Do you want a broody to raise chicks with the flock? A broody needs sufficient room to work with.
14. The more space you have, the easier it is to integrate chickens. Chickens have developed a way to live together in a flock. It’s called the pecking order. But establishing that pecking order can sometimes be pretty violent. One method they use to take most of the danger out of establishing the pecking order is that the weaker runs away from the stronger when there is a confrontation or they just avoid the stronger to start with. They need room to run away and avoid.
15. The more space you have the more flexibility you have dealing with problems or altering your management techniques. That’s just basic.
I'm sure I am missing several components, but the point I'm trying to make is that we all have different conditions. There is no magic number that suits us all. I generally cringe when I see a post asking “How many chickens can I shoehorn into this size space?” I think the better way to look at it is to first decide how many chickens you want, then ask “How can I provide sufficient space?”
Some people consider giving chickens extra space to be coddling the chickens. Let’s examine that. If I give them extra space I have to deal with fewer behavior problems, I have more flexibility in managing them or in dealing with problems that come up, and I don’t have to work as hard. Is that coddling the chickens or is that not going out of my way to make my life harder than it has to be?