Well, curvy girls are usually anyone 170 lbs plus.. Now my ex gf's were both curvy they were both over 200 lbs. Some could call a certain few of who I dated to be considered overweight, but it made no difference to me.
This is a bit of a general chart, but it gives you a good idea of whereabouts you should be, based on your height.
In reality though, things are never that straight forward.This chart doesn't take into account things like muscle mass for example.