I have 2 silkie bantams and a jap. banty the jap and one of silkies are chicks right now but the other silkies is 12 weeks and outside. She is only 4 oz. and full grown!!! My other chickens all outweigh her by atleast 2 pounds!!! So I was thinking I needed to build them there own coop and run. I know it is 10 or 4 sq ft per bird but does that same rule still apply for banties???if not what is the rule of thumb for them???