There indeed ARE too many variables to say what size you should wear at what weight. If you have two women who weigh 180 pounds, and one is 5'1" and the other is 5'7"...the 5'7" woman is going to look a lot thinner, and be in a smaller size because she is half a foot taller.
Also-your body TYPE will often have a major impact on WHERE you lose fat first. There was the comment about tummy fat being the last to go...this is usually only true on "apple" or "cylindar" body types-where the tummy is a problem area. On hourglasses and pears...we lose in our faces and tummies/waists quite easily at first...an keep our rear ends until the end.
For instance-before this pregnancy, when I went from 211 to about 165-I lost an average of 1"-3" all over my body-each thigh, my hips, upper arms, bust, and so forth...but I lost 7" in my abs/waist.
Many women here can weigh 140 pounds, for instance-and be anywhere from a size 14 to a size 4, depending on their build, height, amount of muscle mass, body fat percentage, body TYPE, and other factors.