How do you get a girl to tell you how big her boobs are?

Is there a trick question I can ask or do I just have to peek at her bra tag when she isn't looking?How do you get a girl to tell you how big her boobs are?
Pervert. :How do you get a girl to tell you how big her boobs are?
|Ask her so she can slap you in your face.
there are 2 ways black mail ( my favorite ) or money