probably 3 or 4 if they get free range maybe a few more but not to many mine has a large run on it so I was able to fit 11 hens in mine and they are fine with each other and I don't have any picking or fighting.
Henry
Looks great 1/2 inch hardware cloth is much better at keeping predators out then chickens wire also the 4x4 wire will allow predators to get in.
Good Luck nice tractor,
Henry