I'm a men's size 10.5 and the large size fits perfectly. They're very comfy.These are heavy socks, definitely winter socks, at least for me. My feet get hot and need to breathe, so much so that I wear sandals year round. Yes, I'm a socks and sandals guy and not ashamed at all. Typically in summer I'll wear non-padded running socks as they breathe well. As the weather cools I'll switch to warmer/thicker socks. I tried these recently on a cold morning (35F.I'm in the high desert) and they're comfortable when not doing anything. Honestly probably too warm for any actual activity (like hiking, skiing, etc as suggested).The quality is slightly lower than that of Smart Wool or Darn Tough. They don't seem to have as much wool (despite claiming about the same blend) and they don't breathe as well as I'd like (hence 4 stars not 5). However, I think they'll be good for cold winter days. I don't wear shoes inside and they're definitely around the house. And for the price, when compared to the aforementioned brands, they're probably worth it.