You should get the bra size that is most comfortable and supportive for you. This depends on the measurement around your rib cage (under your breasts) and around your breasts.
You can call your girlfriend and ask for her bra size. If you aren't comfortable asking her, then buy her something that is not a bra.
If your bra makes it hard to breath in, you should wear a larger band size bra. If your boobs don't fit in the cups of your bra, you should wear a larger cup size.
Get yourself fitted.
Find yourself adjusting your plus size bra's straps in a futile attempt to keep your breasts from sagging in your new bra? If so, then like most women, you are wearing the wrong size bra. Your plus size bra should support your breasts with the band and cups, not with the shoulder straps. The next time that you are shopping for plus size bras, you should rethink your bra size. Try on a larger cup size and a smaller band size than what your current bra is sized. Latch your plus size bra on the middle hook and see if it is supporting your breasts.
padded bra
You could measure it. if there are tags on the bra that tell you, then look for it.
you can get a bra measure from primark
it should be around 30
Yes there is, victoria secret sells this size of bra. There are also plenty of other sites where you will be able to buy a bra of this size. You should be able to just go to your local Sears or JC penny's to find this bra size.
depends on your age
if it fits
There is no ideal bra size for a 12 year old. Your bra size will change a lot over the next 8 years, and probably over your entire life.