Mine is 8x8 inside a run of 12x24.
The problem is that noone thinks of "vertical"space.
chickens dont remain on the ground 24/7. unless you have a miserable coop and run without perches. my coop and run cieling is 7' high at the peak. It also has rafters where the game hens go and sleep.so with them biters out of the way,there is alot more room.Also since my run is covered now do to winter, most of the chickens,both ducks,and 4 guineas sleep in the run. They sleep on the wooden sawhorses I built. One problem is that I have a pullet barred rock that was hatched with her oeg bantam pullet/friend and they both sleep in the rafters.All the rafters and perches are 3x3's from pine pallet wood as is the coop and run. I have enough room to put 2 dozen more hens in there considering the vertical space.