Fits most housecats or 6 year-old children, maybe!  Adult humans?  No way!

CAVEAT EMPTOR!  This hat is a complete waste of money.

The cap I received not only didn't fit me.  It didn't come CLOSE to fitting me, even opened up all the way.  I have a 7-1/2" head (on the larger end of the spectrum).  It also didn't fit any of my male coworkers, even those with smaller heads.

Edit: Reading other reviews, it seems many people had the opposite experience I had, receiving hats that are way too big.  Could there be that much variety in their product sizing?  There are other reviews where people received velcro adjustment straps.  Is it possible they just have a big bin of mixed and matched caps that they're dumping off on people?

Really, go with a different cap.  I found a nice large-size fitted cap (here on Amazon) that's way nicer than this one, for $9.99 and although it wasn't Prime-eligible, it fits me perfectly, and I love it.

Link: http://www.amazon.com/gp/product/B008CJ4MU0/