Four square feet per bird inside the coop is not a minimum, it is the most space they need to be the most happy. Some people go with two square feet per hen in the coop, and they do completely fine because they have plenty of outside space. (recommended 9-10 sq.ft. per bird, which
is a pretty good minimum.) I go with 2.5 - 3sq.ft. per hen here, and they are all just fine, (although, mine aren't yet full grown and there is room for two or three more, if I go with 3 sq.ft.,... so...).
Anyway, my point is this: with a coop floor space of 4x8, or 32sq.ft., and a run of 8x16, or 128sq.ft., and you give each hen:
4sq.ft. 8 hens 10sq.ft. 12-13 hens Great
3.5sq.ft. 9 hens 10sq.ft. 12-13 hens Good
3sq.ft. 10-11 hens 10sq.ft. 12-13 hens O.K.
2.5sq.ft. 12-13 hens 10sq.ft. 12-13 hens Eh...
2sq.ft. 15 hens 9sq.ft. 14 hens Uncomfortable
Of course, more birds means in a smaller space means cleaning more frequently. And of course, you should give them as much outside room as possible, even if that means tacking on a less secure run to the pre -existing one, and opening it every day, or letting them free range sometimes. If you are mixing young pullets with the older girls, each extra inch of outside space will be appreciated, along with hanging treats and hidy-holes to distract everyone until things calm down.
Hope this helps.
