I ordered a size 1 for my son but the tag on the water shoes that arrived said size 12. They fit him, anyway, which was very weird to me. It's not even a UK/US conversion since a youth size US 1 would be a UK youth 13 (not 12). He said they were a little tight but his toes were not scrunched up so he decided to keep them. He used them for swimming in the pool for one week at cub scout camp.