A quick, easy way to find your bra size? What is your chest measurement? get one in that band width in an A cup and it will fit, be small, or be large, if small, get a B, if big, pad it or try to find an AA in the band width. something like a 36 band width will come in about anything from A to DD, so no problem. when you go above 38 though, sizes usually start in B or C and go up from there in the common stores, a bit large for most. I sometimes find a 40 B and when I do, I pick up a couple or three, as if you wait until you need a new bra, you won't be able to find anything less then a C which personally I could go swimming in.
If you are fit and trim, you can go with a smaller band, so if 40-44 you can go with a 38 A or B with little if any unsightlyness, but if carrying extra weight on the back and under the arms, doing such a thing will make you roll over the band and look horrible in a close fitting top. The darn things streatch pretty good, but more then a couple or few inches is asking a bit much, especially in the confort zone. If you can't keep the straps from falling down over your shoulder without making it to tight, pull the straps together in the back to lap them over and fasten them together with a small safety pin, this also works to add a little "perk". Generally, the smaller the bandwidth of course, the more range in cups you have and the larger band widths assume a large cup. Finding a 40 A can be an all day hunt if you get lucky or go to a specialty shop.
Hell, I preferr a dark colored "wife beater" worn braless, but then I'm wicked at times, I waited all those years to grow em, so sometimes I'm just juvenile enough to show em off. Bras are for when you have to go somewhere or work in order to protect the boys from chewing thier fingertips off. Personally, I get a kick out of fingerless males.
Terri