Each additional guinea pig in the environment should add a minimum size of 1.5 square feet to the habitat size, which means the cage for 3 guinea pigs should be 9 square feet, 4 guinea pigs should have 10.5 square feet and so on.ou will need a cage that provides at least 7.5 square feet of flat open space for 1-2 guinea pigs, with an additional 1.5 square feet of flat open running space for each additional guinea pig in the same habitat.