I usually wear US 8.5-9.5 mens running shoes depending on the type and brand of shoes. Since I wanted to wear these shoes without socks, I chose a size 8-8.5. and they fit well. However, I can't decide if they are big because the top of the shoe doesn't touch my foot and when I walk fast (almost jog) I feel like I'm about to walk out of NB I have a lot thin feet. There is enough space in the toe area and they are not tight on the heel. Sometimes I can climb into them to put them on. I haven't worn them in the rain and don't think I plan to pack light. I walked around the island of Capri in these shoes for a day once and was fine (I only walked about four miles though). When I normally wear them it's only three or maybe four hours at a time to give context to this review.