How big do German shepherds get?

I was just wondering how big the average GSD gets(not the purposely bred over-sized giant ones) I'm asking this because my mom uses their "size" as the reason that I can't get one. From what I've seen/now they don't appear to get as big as my mom thinks, she thinks they get HUGE, mostly due to the fact that my sister and her ex had one that was GIANT, like if you've even saw an english mastiff, THAT kind of huge. But when I see the police GSD they look about the size of our american pitbull.