Wow, this really helped me because I'm having such issues with my weight loss and visualizing sizes.
I just dipped below 250 (it's not thin but is nice to say I'm 247!) and I'm in an 18. I have already bought a size 16 and I'm hoping to get into that by Christmas. My tops are either an XL or 1X. The weight loss has slowed and I don't wear anything too tight, but I think every 20lbs or so for me is another size.