It depends on the jean- the sizes run differently- just an FYI- Paige denim goes all the way up to a size 34- I think thats the largest in designer denim
yea, I'm a size 12 in regular jeans and in designer jeans, I wear a size 32.
I have found these brands fit me (am a size 12):
AG, Joe's, Christopher Blue, Goldsign