I'm normally a 12.5 or a 12W -- altho I usually find myself having to buy size 13. These slippers fit tightly on me like a true 12, so I'd say the sizing is spot-on. In my particular case, this tightness generates extra warmth. If you're a true size 12, these will be the perfect snugness. I've had slippers before that were a 13, and that extra 3/4" or so made the slipper too loose, and as a result the warmth was compromised.

These are pretty warm overall and quite a value at $15 or so. My only "complaint" might be a questionable durability. I just got them a few days ago and I don't get the impression that I'll have this same pair a year or 2 from now. As another reviewer said, you can not slip these on -- they require two hands.