I run a 10.5 for most shoes but a 10 for dress shoes where I typically wear thinner socks or don't have athletic shoe padding. Since these are slipper-like shoes that I wanted to wear without socks, I ordered my "dress shoes" in size 10. My healing crept out a bit. A friend who had many of Tom's shoes advised me to go down a size because they stretched out around my foot. I went back and ordered a 9.5...a whole size smaller than I think my shoe size is! And sits firmly, the heel no longer slips. I don't think I'll read a review and ever order a size smaller... but this is my review or at least half a size smaller than your shoes.