I ordered one for me and one for my husband, and they fit perfectly!  The white one dirties a little too easily and has to be wiped down periodically to keep it looking white instead of ash gray.  The yellow one hides dirt a little better but again, light color needs cleaning more often.

And now for the fit and function.  All I can say is, I usually wear Crocs Athens W8 (M6) and the size 7 (39-40) fits PERFECTLY.  They're a little small for my husband but absolutely perfect for me.  Now, the material itself is SO SOFT it's like an anti fatigue mat on your feet, it's so rubbery soft yet strong enough to resist average wear and tear.  The rubber springs back with each step, truly like putting that proverbial spring back in your step.  You don't feel tired walking in these like you may in in normal slippers (flip flops) or if you get a weird pair of crocs Athens with too big an arch or something built into the footbed.

The slipper is really comfortable, and another perk is the bright, sunny, and cheery colors, like when Crocs Athens still came in lime green, red, orange, yellow, and pale blue.  Remember those days?  Also these Havaianas aren't as bulky as the Crocs, and you can put them neatly into a backpack without taking up as much space as Crocs do.

Really nice, luxuriously soft, springy, comfortable, durable, and brilliant colors!  Can't find a thing to complain about!