I wear a size 11. There was no way to size up, and I can usually get away with a 10 or 10.5 in a sandal. I tried 2 different pairs, but they were both a bit too small, and the cords were a little tight. I have pretty average width feet, so I don't think that was the issue. I think a half size more would usve worked...but sadly, they don't really make them in a higher size.