I normally wear size 9.5-10 shoes, so first tried size 9 slippers, as per the recommended fitting advice, but it was almost painful to try and get my feet in. Ended up going for size 10, which is very snug with thin wool socks as they don't seem to bed in that much. They are very cosy, sturdy and well made, although I could use a little more wiggle-room around my toes to air out, as they end up getting sweaty and a little cold after a while. Overall very happy with them and they look like they will last a lot longer than a much cheaper pair of wool slippers which were lacking a proper hard outer sole like these ones. They are expensive though.