As applied to LF laying or breeding chickens:
It seems I see this more and more. Always the questions of how do I fit all the chickens I want into this space. The questions are fine....but many times we see that people will already have a certain number of chickens on the way and then ask the question of space. Many times the over crowding then leads people to ask what is wrong with them when they get sick. What is usually wrong is that their owners wanted to satisfy their desire for a certain number of birds more than they wanted to raise healthy and happy chickens!! In this world today we have been taught that there is always a way to satisfy our wants no matter what it takes. (we are a very spoiled society with entitlement issues). Sometimes we are just going to have to admit that it can not be done!
By the time you get in the feeders, nest boxes, waterers, roosts, etc.etc. You need 5 sq./ft per bird inside with a minimum of 32 sq./ft. (no matter how many birds you have). You need 15 sq./ft per bird of run space (ONLY IF THEY CAN FREE RANGE SEVERAL TIMES PER WEEK) If they can never free range...then you need about a 100 sq.ft. per bird of run space. Just measure the length and the width of the coop floor and multiply those together. Take that answer and divide by 5. That is how many chickens you might be able to have. Now measure the length and width of the run space and multiply. Now divide by 15. Look at this # and the # from the coop space....take the lowest #. That is it....that is the # of chickens you can get (period) Get more at your own risk!!
Chicken tractors were invented to allow the controlled and safe ranging of chickens, not as a permanent coop. The same sq./ft. rule applies to tractors. A tractor is outside and therefor figured as run space. If you have a 32 sq.ft. tractor (4 x 8)...then you can only get 2 birds in there to roll them around so they can have their outside time and pick at greenery and bugs during the day. As sun set approaches they need to be back in the coop.
You may berate me for this, you may not like it, you may think I'm mean, etc.
Regardless of how you feel though, that is the way it is unless you and your birds wish to suffer the consequences of any number of problems.
I imagine that there will be plenty of people that say they get away with much less space and not had big problems...this might be correct. But I think you will find as time goes by these folks are spending an inordinate amount of money and/or time trying to avoid problems. Me? I like being able to just do a couple cleans a year, having a coop that never smells and having happy and healthy chickens without having to constantly solve problems of pecking, fighting, disease, parasites, and the list goes on and on. So these are my opinions formed by countless mistakes in the past. For the folks that want to say to look at the commercial operations and their space...would you want to eat those so called eggs? For the folks that say it has been done with much less space for hundreds of years, or "my grandfather did it such and such a way".100 years ago most chickens did not make it past 2 years old, nor produced the amount or quality of eggs.