With chickens free ranging during the day, I think you will be O.K.!
To get square feet:
3x4=12 then divide by 4
so 4 goes into 12, 3 times (you can fit 3 chickens)
Chicken needs:
4 square feet in coop & 8 square feet outside
Soooo Cute!!!
I am wondering how old chickens are & what kind?
I am asking this because it is a bit tight for 6 chickens! ((unless they are bantams))
you could put a cover over your run so they can access in any weather (that would give you more living space!