I ordered a full size larger than my usual shoe size and the fit is perfect with thin socks. Don't really need heavy socks due to the ample insulation. Like heavy socks? Add another half or full size. If these Grition hiking boots don't fall apart I will buy at least one more pair and recommend them to everyone I see on the trail. The built in arch support is perfect for my flat feet. A pair of $7 Hon Plume inserts for flat feet makes these one of the most comfortable pairs of footwear my feet have had the pleasure of wearing. Just a very nice pair of boots.