I wear a 10.5 in Nikes most of the time, but I read that these can be a bit snug, so I went with an 11, and that worked out great. They may be too warm for hotter months due to the strange sock thing on the inside, but I could see that being a huge benefit to someone that would be hiking with them. I just bought them because they remind me of Unit 02. I might buy another pair in black or purple depending on how these break in.