it can really vary dependign on how you carry the weight, i am 12stone8 and 5ft 11 and in size 16 tops and bottoms and i know of one lady who is 5 inches shorter and the same weight and in a size 12-14.
Im 5'10 and 14 stone and a size 18/20 bottom and 16 top. I seem to carry all my weight in saddle bags on my thighs so it does very much depend on how you carry the weight!
Lets buddy and try to reach size 16 together. I have given myself 2 weeks although its probably optimistic at least its something to aim for.
What do you think?