I've been on a quest to find a sport sandal for my skinny, long-toed, small-boned, slightly narrow 10 1/4" feet. I wear a 10 in shoes, usually a Medium. In sport sandals, I'm finding that narrows are almost non-existant and that many brands run long. I tried these a whole size down from my normal shoe size and they JUST fit. In other words, the strap, pulled as tight as it can go, is just tight enough to keep these on. I don't know if these run long for everyone or just me, but there you go. YMMV. I also have a highish arch and these seem made for low-medium arches with good support. I ordered some Chacos Updraft X2 at the same time and they definitely have higher arch support, so I am going to try them a full size down and see if I get a similar result with the long strap.