Medium size is for either Ladies shoe size 6-9 or Mens shoe size 4-7. 

Large size is for either Ladies shoe size 10-13 or Mens shoe size 8-11

Great for Diabetics or anyone who wants a loose fit at the top of a sock. The best sock you've ever put on your feet. Anyone who wants a comfortable and environmentally sustainable sock should try this non-confining sock. They are particularly great for anyone with ankle swelling. Top of sock is goes from a normal circumference to 17 inches when fully expanded. They provide great relief to people who are tired of socks that leave indentations on swollen ankles. Socks are not returnable. Chat with a Fit Specialist to ensure you get the right size for your foot needs.