Several factors go into this. Height, weight, body frame, type of clothing you wear (every brand's sizing differs) You must know your body and go from there. Maybe keep a journal so you know what weight you need to be at to fit the size clothes you want to be in.

Everyone is right, it really depends on body frame, etc. I just wanted to add that it can also vary greatly on the same person. About 10 years ago I went on a severely calorie restricted diet and did not exercise much at all. I managed to get down to about 122 pounds (but obviously I was miserable and starving and promptly gained it back). I still have the size 8's that I was wearing when I was 122 pounds, and I've tried them on but they are way too big for me to wear now even though I am over 20 pounds heavier. I now wear 4's and even some of those are baggy. The difference is that this time I lost the weight by eating a lot of healthy food along with lots of exercise, so I'm sure my body composition is very different than it was back then. Plus, even though I'm just maintaining now, I am still toning and tightening up with all the exercise, so my clothes just keep getting bigger on me. I still get the "wow, you are just getting skinnier every day" comments even though I'm not losing anything and haven't been for a while.

it's weird...

I weigh over 160 pounds (I'm 5'7) and fit into a lot of 8's, but mostly 10's. I have a lot of muscle tone so that definitely attributes to it...

I'm 5'2.5" and fit into a 4 when I was 120 - we don't need to go into what I fit into now!

I'm a size four, and fit into fours ranging from 115-139

Edit: I'm 5'4

I am a size 12 at 184 pounds, when I was 199 I was a 14/13. I think it all depends on your body type, muscle mass, bone structure. The way you eat and the amount and type of exercise you are doing all plays an important factor in the way your body shape forms. I believe that for about every 12 pounds you lose you should lose a dress size!

Right now I am 5'7 and 154 pounds ..I am in a size 10....I want to be down to a 5/6..which will probably be when I am 130-135


But when I started my weight was 175 and I was a size 12...even after 21 pounds I only lost one dress size....but it was because I lost the weight all over and I am very small boned....when I was 5'7 in high school and weighed 138 I was in a size 7/8...so the next 20 pounds lost will be better for me

I'm 5'7" and 165 or so. I'm comfortable in 12s but can squeeze into 10s or even some 8s -- my belly ooozes out in the lower sizes.

At my lowest 125 I was a 6/7.

umm ok i'm 5'5" and currently in a size 16 at 185 pounds and at my lowest i was 120/129 i wore a size 11/12

I am 5'9" and at between 145 and 150 lbs. I am either a size 6 or a size 8 depending on the brand/cut. I wear a size 4 in skirts though (no idea why this is different).

I have a friend who is 5'2", though, and at between 110 and 120 pounds she fits in a size 2. So, at around 5'3" i think you could be a size 4 between 125 and 130 lbs. (again, as everybody else has said...depends on your build).