I buy these thongs every year.  They are absolutely the most comfortable flip flop I have ever found. I traveled by RV for two weeks in Nebraska, South Dakota and Wyoming going to the Badlands and Mt. Rushmore and wore these the whole time!  My feet did not hurt.  They do not slide off, they do do not turn in or out on my foot, and they stand up to wet weather great!  I have gotten atleast 2 seasons out of each pair.  My son takes them on me now too!!!
I wear a 7 1/2 in sneakers and in these I wear a 7, with a little room at the front and the back. My feet are not hanging off at all any wear.  I have a somewhat wide foot and the width is great.  If your foot was really really narrow, these would be too wide for you.  I would say they fit average width to slightly wide.  Can't go wrong with this purchase, however, I pay about $15-$25 for them at "f.... L...."  this price is way to high!!!