Definitely size down. Normally wear an 8.5 so naturally I thought to size up if in between. SHUCKS! I wish I had gotten the right size! I rated the product based on how it fit me, however I can tell I will love it once I re-order.  The products fit was large so  honestly couldn't wear them for than an hour. The width despite it being to large fit fine and I really couldn't tell if it had good arch support because it was too large. I am sure they would have though...Hopefully I love it the second time around =)