How many lbs to drop a dress size?

 I agree. The "plus sizes" seem to take quite a bit more pounds lost in order to move down. After that, I think that roughly ten pounds seems about right. I remember (way back in the day) when I'd loose three pounds and my clothes got loose, but when I was wearing a 32, it took a good 20 pounds or more to make a difference. 

I wish there were a good answer... For me, I lost 25 or so lbs and went from a 24 to a 16. Then it's taken me 60 more lbs to go from a 16 to a 12.  So it has gotten slower for me as I've gone down in sizes.

I've come to the conclusion that when I hear that someone's "lost 6 dress sizes" that actually means they've gone from, say, a 24 to an 18 (24 minus 18 = 6).  Whereas, I would only consider that THREE sizes, since sizes (at least in Canada) go up by two's - 18, 20, 22, 24, etc.  I've gone from a tight 24 to a 16, and I say I've lost 4 sizes.  Bottom line, I seem to lose a size every 20 lbs.  In Kelly Osborne's case, she's obviously counting (for example) a 13/14 as two sizes.