GO GET MEASURED! First and foremost that is the thing to do because it will help you in the long run. I am one cup size bigger than what mostly all my bras are now. I never knew how uncomfortable it was to have such a small bra cup size and if you are bigger chested woman than you should know how uncomfortable one size to small is. I am a smaller chested woman and it may not be important but it is, I swear.
Don’t know where to go get measured? Go to Victoria Secret, Lane Bryant, Aerie or any place that specializes in bras or lingerie. It may be embarrassing but think about it this way; they measure women every day from all ages. Any associate with a tape measure around their neck will be able to help you or they can go grab one but they most likely will have one around their neck.
Bra types are important too. If you have bigger breasts I would not go with a demi from Victoria Secret unless you find the full-coverage demi. Full coverage is better for bigger breasts and will keep the girls inside. If you have smaller breasts it should be fine to get a demi. I would also try the bra on, not matter if you know your cup size or not you need to make sure it doesn’t hug you in the wrong places because some bras will.
All women are different and if you can find someone who can explain it all to you, the different bra sizes and kinds of bras will give you a much bigger insight to what is right for you.