Most sources recommend the space requirements ber bird
Standard sized chickens: 4sq feet
Bantam sized chickens: 2sq feet
If your chicken house is 8ft x 8ft, then you have 64sq feet of space. Therefore you could house 32 bantams or 16 standard sized chickens in your chicken house.
Incidentally, my chicken house is also 8x8. I house 14 bantam cochins in mine. Technically, I could comfortably double the number of birds I keep accroding to the space requirements listed above.