I have other Vionic sandals in size 9 and so I ordered size 9 for these.  I could fit an entire finger behind my heel - way too big.  Also the arch was painful when walking, not like the sandals I have which I could wear all day without problems.  On this shoe when my arch tendon flexed, it hit the shoe's arch and hurt.  I could barely walk down the hall in these.  I had to return them, which cost me $14 in shipping fees...hoping to see that refunded when I get my money back (shouldn't be a problem).  They were VERY cute, however, and I really had hoped they would fit right.  My suggestion - find these in a store to try them on for size.