the sizes refer to the cushion part of the shoe.  however the bottom blue part actual extends the shoe and makes it a whole size larger overall.  unless your foot is a perfect match for this flip flop, it may feel a little awkward especially since the shape of the cushion leaves no room for error.  if your heal is to big or the flip flop is too small, the back rim of the cushion jabs into your heal and shoots pains all the way to your spine.  However, I would recommend at least trying this one out.  amazon probably will pay to ship it back if its not satisfactory.  They did that for me.  Excellent service by amazon.com, but this flip flop is a hit or miss. (round up your size when going for this one 8.5-->9)