Is my bra measurement weird?

I'm 16, caucasian (but with swedish ancestors) and I am a 40B. The 40 is the measurement of inches around my ribcage just below my , and the B is my cup size, right? That just seems really odd cuz all I've heard is like 32B and 36A nothing close to 40. I have to wear a bra extender so it fits around my ribcage. Am I just big-boned or what?