Safe grids are 14” x 14” with 9 holes across, 9 holes down. Openings should be less than 1 ½” for adult guinea pigs. For young or baby guinea pigs, you’ll need to temporarily baby-proof the cage so they can’t reach the grids as they could be tempted to poke their heads through and get themselves stuck. So it’s recommended to put coroplast or cardboard around the cage at least 9” high temporarily until they reach adult size – generally over 9 months. We also have available our Pig-a-Boo clear half windows that can be attached to the grids for safety.