I bought a 10 because I wear a 9.5 size normally.  I assumed they would actually be a bit big but they fit more like a 9 because my foot was right at the end of the flip flop.  I was disappointed about that.  They were also not very comfortable.  I bought them because we were going to an indoor water park and they were perfect for that purpose.  They were definitely good as water shoes and dry quickly.