for the men's shoe i bought:
i bought the size 11 for my 10.5 sized husband, and after ordering both the 11 and then the size 10, the smaller size would have been the better 1st purchase. maybe a 9.5 would even work for him, but we stopped at the second purchase.  whatever you do, don't round up a size.

DONT USE THE CUDAS WEBSITE.  i ordered and paid on the 24th, and they didn't postmark his shoes until the 8th!!! and there is NO contact number on the site!!!! (which means NO CUSTOMER SERVICE).  there is just a form to fill out if you want an email reply, which they NEVER replied to.

i wrote this for the women's version:
two main things you should know before you buy: 1) the khaki color is actually a light green, and 2) they run at least a full size large. i had searched the web looking for reviews on this shoe, but only found one, which told me the same thing (so now there are two reviews on the web that say ORDER A SIZE DOWN). i am usually a 7- 7.5, but the 7 is much too big to wear in the water.

on close inspection, these shoes aren't as cute as the picture makes them look, but for 20 to 30 dollar water shoes that will protect my precious feet from the coral beaches here on okinawa, i think it isn't a bad deal. the rubber sole is clear and you can see the material through it, but again that shouldnt be an issue.

update: i bought the 6 in navy, and it fits perfectly.