well, I have a size 8.5 wide to 9 shoe. I've had my Lightning bolt XL jets since 1986. Love em... used with hard soled 5mm dive booties and a dry suit with way too large rubber booties that squished in quite well. Just picked up a dui cf200 dry with size 11 rock boots. the 11 should be too big (for me) but with socks and the DUI crushed neo they seem to fit my foot OK. The size 11 rock boot does seem to be pushing the limit of my Jet fins. I'm thinking of picking up size 10 all stars and spring straps. Oh I'm just going on here aren't I. Short story, Size 10 foot? need XL for minimum exposure protection and larger for things like rock boots. Although I have read that the pocket shape and size has changed over the years. I have never heard anyone say it was shaped like the human foot. I have heard stories of heat guns ( I won't go there either).