Go size smaller!! I wear 8 to 8 1/2 I need a 38 in women's Birkenstock. Love these shoes! They are helping my back and legs and hips and cute. Toe post taking some getting used to as it is very thick. This is my first try with Birkenstock. I got carried away and ordered 3 pair(2 styles) which are all too big because I ordered the 39(which shows it SHOULD be right). I am urging my daughter with bigger feet to wear them as I can't return them after wearing(please don't you do it either.. GROSS)** I have now gotten 3 pairs of the 38M and they are perfect for me where the toe bar hits and just enough room in footbed.  Free shipping and returns with Amazon means you should try a couple sizes to be sure.  When they fit the way they should these shoes are incredible once you get them broken in.