This poses a good question really, about where we all carry our excess weight. Mine is on my bum/hips/thighs. I have a small waist, which only accentuates my large bum.
In answer to the question, when I am around 14 stone I am in an 18 (or was pre having a baby, been a while since an 18 has gone over my knees lol).
At my lowest weight of 11.5 stone (8 years ago) I was a small 16 bottom and a 14 top, with a lovely flat tummy. Oh, the memories....
That's what I am hoping for again. A 14 all over would be grand, but if I can't do it, then a 14-16 is perfect for my build.