I wear a 9.5 in Revas and anywhere from a 40 to 41 in European sized shoes. So for me, I went down a size/half size. They are somewhat generous but you should be mindful of how much the elastic on the heel will bother you. At first I couldn't decide if the 9.5 was too big or too small (which is ridiculous, of course). The elastic in the heel wasn't at all stretched, but still felt like it dug in a bit. They were a bit uncomfortable in the heel the first couple of times that I wore them, but few problems after that.