How big should a guinea pig cage for two be?

7.5 sq ftmore is better30" x 36"2x3 grids27" x 41" 7.5 sq ft10.5 sq feet 30" x 50"2x4 grids27" x 56"10.5 sq ft 13 sq feet30" x 62"2x5 grids27" x 71" 13 sq ftmore is better30" x 76"2x6 grids27" x 84"