This is my third pair of Birkenstocks, and since I started wearing this brand, I don't want to wear anything else for more than an hour or two.  However, even though I bought this pair in the same size as the other two, they seem bigger.  They don't stay on my feet as well.  I hasten to add that they stay on my feet anyway because I don't want anything else on.  The shoe top material is beautiful.  I feel well dressed when I wear them.
Of course, Amazon service is impeccable, as always.