I’ve read anything from 7” to 24” per chicken on here, quite a range. Most of the time when people give you these numbers they don’t take anything into consideration as to why different numbers might work. I’m not going to give you any magic numbers but will mention some considerations.
As Mary said, they can crowd together but they need room to fly up. As June said, in hot weather they normally spread out more than in colder weather if they have room and bigger chickens take up more room. Those are important points.
I suggest you also consider your comfort and convenience. Will you be picking chickens off the roosts at night for inspection or other considerations? How will the roost locations and types affect your cleaning? If you use droppings boards how are these set up?
Different spots on the roosts are preferred over others for various reasons. Mine like to sleep near the window. Higher points are usually preferred. The chickens at the top of the pecking order get to sleep wherever they wish, the others have to make do. It can be kind of rough and tumble when they are settling in for the night, even with an established flock. It’s not totally unusual for mine to knock each other off the roosts when a higher ranked chicken I trying to get to a preferred spot and a lower ranked chicken is in the way. If you are integrating new chickens or raising chicks with the flock, it can get even rougher.
Some people want all the roosts at the same elevation, others don’t and are quite successful using a ladder type roost. Both can work, plenty of people on this forum have proved that. Dad used a ladder-type roost and they worked fine. But we all have our preferences.
The time mine are most brutal to each other is when they are settling down on the roosts at night. During the day I don’t have these issues, probably because they can spread out then while on the roosts they are kind of packed together. Usually this involves a hen that outranks another, especially when I’m integrating less mature chickens. The higher raking hen may peck the lower ranking just for being next to her. It normally doesn’t happen in a fully mature flock, but isn’t rare at all when I’m integrating younger chickens. I’ve seen a mature hen walk to the end of the roost to peck an immature chicken. From reading your post about your numbers fluctuating and culling, I think this may be an important consideration for you.
With my flock I’ve noticed that the highest ranking chickens tend to sleep together in the preferred spot. The lowest ranking chickens tend to sleep at the far end of my roosts, as far away as they can get. The ones that rank in the middle tend to sleep in the middle.
Broody hens usually take their chicks to the roosts and protect them, but after they are weaned, the chicks are on their own. Sometimes they stay up there, sometimes they leave. If I have immature brooder-raised chickens, they avoid the main roosts entirely until they mature enough to force their way into the pecking order. With pullets this is usually about the time they start laying. Who knows when it will be with cockerels? Until then, they get picked on so brutally they avoid the main roosts and look for a safer place to sleep. This is a big reason some chickens sleep in nests, they are safer than sleeping on the main roosts.
I don’t believe in number of inches per chicken, I’m more into quality of space and your flock considerations. If your flock is all mature chickens that are fully integrated you don’t need as much room as you do with a mixed age flock. They are normally quite happy to crowd together once they get settle in.
My numbers fluctuate a lot more than yours. My main laying/breeding flock is normally around one rooster and 7 to 8 hens. But I practically always have immature chickens mixed in being raised to butcher age or being evaluated as replacement layers or a replacement rooster. It’s not that unusual for these numbers to peak in the 30’s in there, though most of them are pretty young and usually not sleeping on the adult roosts.
My coop has two main roosts across the back, about 5’ high. This is for the adults. I set up a separate juvenile roost at about 4’ high and horizontally separated from the main roosts. These are higher than my nests so I hardly ever have any issues with them sleeping in the nests.
I don’t know how big your coop is or how it is laid out, but I suggest you give them enough room so they can get away from each other if they wish, and if you see a sleeping in the nest problem, consider adding a separate juvenile roost. You could put one in now, but as a minimum consider how you would add one in if you see a need.
I know, a lot of rambling this morning but hopefully you can get something useful out of it.
