You can 't unless you measure her,or she tells you. Depending on age don't ask her.
I doNt know the average, but I am 16 and my bra size is 34B and my girlfriends is the same ( i an a bisexual)
Someone can only tell you your bra size if you get someone in a bra fitting store to measure your breasts with your bra on.
just ask her, theres not much other way of finding out
You could measure it. if there are tags on the bra that tell you, then look for it.
when the training bra's start getting too small, or If they have your size in a regular bra.
You don't. That is not something you can eyeball.
You cannot tell a girl's bra size just by looking unless you have years of experience in professional bra fittings. Unless you are planning to buy her a bra, you really don't need to know. Focus on finding out more about her interests instead.
All you have to do to find out your bra size is go to any bra and underwear shop, get your self fitted and buy a bra of your size.
its a big how can i tell ok i think 36d
You can't. All you can do is guess.
It will be a different size everytime you see her, it will be uneven and sometimes look like a square, and if you ask her bra size, she will say a letter that doesnt even exist. (On the bra scale anyway)
you cant have a larg bra size you have a larg bra size