im 21 and i was 203 pounds and a size uk 18 but now im 150 pounds and a size 10 uk. i want to be between a size 6-8. how much more weight will i have to lose and whats a good weight for my height?
There's no way to know what weight you would need to be to fit into that size, it depends on your body shape. If you go simply by BMI standards which isn't really the greatest, a normal weight for you would be between 92 and 123, just a rough estimate.
Size 10 UK? Isn't that like a 6 US? You sound like you're built pretty small for your weight (or muscular?). I know for me, 1 size is about 10lbs once I get down to a size 6 or 8 US.
Everyone carries weight a bit differently. No need to set a specific goal, just eat maintenance if you're satisfied with your loss.
Here is a great link to My Body Gallery. I already put in 4'11" so you can see how different the same height with different weights can look on different bodies.