I'm a size 9, so I ordered a 9 and they fit PERFECT with thin socks. I wore these all day yesterday. Only problem I have is they slip down a little because they are too wide on my thigh. I am 5'8" slender with long legs, but thick calves/ankles and slightly thicker thighs. If you have skinny legs, these will be very wide on your legs.
Also, they have very little support for your foot arch, so all of your weight is literally on the ball of your foot and will become quite painful if you stand or walk a lot in these.