for a pair of pigs it is two by 4 feet, i would say add a foot to the end per extra piggy (2 x 5 for 3 pigs etc)
It depends on the pigs, most girls can live together really happily in large groups, but some do not like it, and boars often are better in pairs or neutered in a group of girls, but as i said the number of pigs kept together depends on personalities.
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