I got these because of an injured toe that requires a lot of room inside a shoe. I normally wear size 11, and I figured that I could use just one of these for the foot with the bad toe. No Need, as these are most definitely NOT size 13 on the inside. They fit both my feet with just a little extra room, so I'd say that they are size 11.5, or maybe a small 12. I think that part of the problem is that they lined the entire inside - not just the sole - of the slippers with a thick, soft, non-removabSee full review