I don't know if you can go by a size. The us has sizes based on inches, and those are even off. I have bought two pairs of the same brand/same size jeans, and they are different.
I base it on height and weight. If your trying to shop for cloths, then I would get out the measuring tape.
And if it helps. I am at 124lb right now, and I ware sizes from a misses 4/6 or juniors size 5 to 9. depending on what brand and style. But, then I still have a gut, so my shirt sizes are a little bigger than my bottom's sizes.
If you want stats on how much you should weigh, then look up some weight charts on the Internet. That might give you an idea. I think there is something like that on here in the calculator section.
I thought you had a really interesting question, femme. I tried looking it up, but got so much conflicting info that I don't feel like I can make an accurate reply! Anything from an average of 140 pounds, to >%50 of women wearing a size 14 or larger. I even saw the two together - but I can't imagine someone at 140 pounds wearing a 14