Khaki Campbells like a lot of space, despite their small size, as they are constantly on the go. It really depends on weather conditions, as they can wreck a pen very quickly in wet weather. if you had 5 or 6 I would have a pen of around 160m2 for winter and half that for summer. I would rotate it as they turn over wet areas, especially round their water but if you are careful, it's semi decent ground, and you don't mind a few messy areas then that size should suffice all year round