Y'know the size/weight thing varies A LOT.
Most people don't believe I weigh what I do (luckily) I tend to somehow stay small.... but I have always been somewhat active, and played fastpitch softball, done yoga and latin dancing among other things.
At the weight I am at now I am about a 16 (ish.... depends on store, occasionally an 18) I wear a womens size 34 jeans.
At about 190-195 lbs I was a 12-14 so working out the approximate math, in theory I should be about a size 8 at my goal weight (160).
My guess is if you want to be an 8, you may have to shoot for about 150, but only way to know is to wait and see
oh.... and in case this helps, I am an hourglass, well I was till I hit about 210.... then my body seemed to give up on distributing it and put it all on my stomach.... from the front I look like an hourglass, but from the side, well..... my stomach sticks out about as far as my chest does (which is pretty impressive considering my bra size....36-38F)