How big should my boobs get...?

oookk. I turn 13 this summer and im goin into 7th grade. My mom is double D naturally and my aunts on my mom size are in the D's too. I'm B30 rite now and every1 always tells me they want my chest cuz their so big lol im 5 foot 1 inch tall and i way 90 pounds. Im pretty thin...on my dad's side, my female relatives are probably C's and my grandma on my dad's size is probably somewhere in the high C's....ANYWAYS, determined on the information i gave you, how big should my breasts be by the time i stop growin??