The sizing charts I have seen for Mizuno are WAY off.  The charts suggest you should buy a Mizuno 1-2 sizes smaller than your normal shoe size.  I wear a 13 in most shoes, but bought a 12 1/2 based on reviews and charts I read.  I had to return them and get the 13, which fit perfectly.  Amazon paid for the return shipment and got the new shoes quickly.  Amazon is always awesome.
The shoes are great for volleyball, esp on wooden surfaces.  On the plastic tile surfaces, they are better than other shoes I've seen, but slip a little.