Ideally, I would wear a 10.5, but I rarely find it, so sometimes 10 works (UGGS), or 11, which was what I bought.  Despite the name (moon boot), this little black boot was surprisingly flattering - not "boat-like" at all - they made my feet look a couple of sizes smaller, and were attractive.  Unfortunately, 11 was just too big - they run wide, so my heel slipped, and they are somewhere between being true on the length and a little large.  At any rate, your feet and ankles will not be crushed by this boot - it's roomy!  It says it's good to -20F, but I can't verify it because I had to return it - it didn't seem overly warm inside the house, but maybe with wool socks.  It's suede, but waterproof, another plus.  The cons:  The footbed could be more comfortable, in part due to the heel being higher than the front, and in part to a fairly firm innersole.  The slender suede tie is awkward to tie it in back, kept coming undone, and seemed flimsy- like it wouldn't last nearly as long as the boot. However, I finally realized that you can just tie it and leave it - there is plenty of room to just slip your feet into the boot without untying it (ever), and a double tie won't untie like a single tie will.  Also, the lining on one boot separated at about the ankle.  Overall, it's a stylish boot, with great features (warmth, waterproofing, spacious, easy to tuck jeans into), that could have a more comfy innersole, but I was sorry to have to return them.