5 and fit perfectly to my foot. These slippers are a warm and welcomed change for my cold feet! Love the shoesSo fun and universalBought them for vacation and just love them I have been using this product since 2012 but I think they just changed the formula. Nomad and Belkin. *Update after using it for a month: use it almost everyday and still love it. Score: 8/10 Wish the cord was a little shorter, but will keep the Twist tie on it. I think Ill eventually try one of 2 options:- (a) tear off that top layer or (b) not use the insoles at all. In less than 4 months (really barely over 3 months) of light to regular wear for work only, these shoes have begun to fall apart.