If your weather warrants them being out in the run most of the time, you can get away with squeezing more birds in small spaces. It is only when they are all stuck in the coop for days on end, all cramped in with nothing to do but pick on each other. I did the same thing on my first batch of chickens, and got more chicks in case I lost any. I didn't, and of course my coop was a bit small for all my birds!!They are all doing great, but now i have a new problem... I got 3 more chicks than i have room for... just in case a few didnt make it ... I have named all of them ... Okay so now what??? I went by the 4 square ft rule in the coop thinking id only keep 6 chickens... but they have a large run of 14 x 6 ft.. My coop is 4x6 but is 6 ft tall and i have 3 external nest boxes... Do I have room for 9 chicks with out over crowding????? I have a friend that will take my 3 extras but now i dont know if i can part with them and which ones do i give up??
But give it a try and see how it goes. Good luck!