I'm an 8.5 and bought these in anthracite in my usual Birk size of 39 - and they fit like a dream. The shoes are super comfy, save for the fact that a piece on the back of the buckle on my right foot only seems to dig into the top of my foot just a touch. And although the shoes are great for summer, they are made of EVA, which makes my feet sweat just a touch. However, I'd wear these any day over flip-flops. They're so much more comfortable, don't make the obnoxious sound that flips make and are great in the sand and for walking about town. (At the beach recently, they didn't fill with sand and didn't flip sand everywhere, either. Win!) Definitely recommend them!