I usually wear a 7.5 or 8.  My general rule is 7.5 for flats, 8 for heels.  Yielding to another reviewer's advice, I ordered a 7.  My main concern when ordering these was that the top canvas-like material would be too loose.  To my surprise, the 7 fit my foot and the material at the top was actually almost too tight (and my ankles are fairly thin).  Unfortunately, just because it zips doesn't mean it's the right size.  The length was too short, which shifted my weight to the balls of my feet and was uncomfortable. I ordered a 7.5 afterward to see if the length was better on that.  It is.  However, the top canvas part IS too loose on the 7.5.  I am returning the 7 and hoping I can make the 7.5 tighter with a little bit of sewing.  I would say definitely don't order an entire size down, but probably half a size.

Notes about the style: I ordered the tan multi and the blue is much more vibrant than displayed.  It's not a sky blue like it appears in the photo.  The shoes themselves are a much lighter weight than I expected.  The front of the sole is a velvet-like material which I don't understand at all because it makes your feet slip on tile, wood, etc. floors, but I am sure it will wear off after outdoor use.  Overall, I'm pretty happy with the purchase.