I'm a woman with size 8.5/9 in shoes so I got the medium in these and they fit perfect! Let me just say, these are sooo thick and warm and comfy and cozy! They washed up fine, but they got a little fuzzy (as to be expected with wool). These are just so great, they kept my feet warm without making them sweaty. They didn't slide down at all either. But unless you have enough room in your shoes, you'll just have to wear these around the house or something because they are SO thick and they can be hard to get shoes on and off. I love a good pair of socks and these seem really durable too. Great buy!