Odds are, you don't truly know your bra size.
How can you tell?
Bra fit tips Any of these poor fit problems look familiar?
bra fit problems

Literally, every bra is sized differently. This means for you to get the best fitting bra, you should first take your measurements and then find out how the bra you want runs (true to size, a bit large, a bit tight) before choosing which size to buy.

Use the links above for more helpful tips on finding the right bra.