I'm a 9-1/2 shoe size and the Large fits me very well. It looks like their sizing chart is right on the money:
Large: 9-12.5, X-Large: 13-16, Medium: 4-8.5

Fit is very important for me since I walk and hike a lot. I'll definitely be putting these through their paces! They are perfect for my low cut hikers.

They are very comfortable and fairly well-padded. Their composition is 82% Cotton, 17% Nylon, 1% Spandex, so they're definitely not very quick drying.

You can wear these over&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/PowerSox-Liners/dp/B00GW7NPES/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">PowerSox Liners</a>. These work together seamlessly! I'm so happy! The liners help to mitigate blisters while the fairly generous padding of these socks provide all-day support and comfort.