You measure under the bust where your bra band goes and add if its 30 inch then you add 4 inch to get 34inch, if its 29 then you add 5 inch. So basically if under bust measurement is odd add 5 inch and if its even add 4 inch.
For cup size measure around the fullest part without squishing them, if the bust measurement is:
same as your bra size, your Cup size is A.
1in. more gives Cup size B
2in. more gives Cup size C
3in. more gives Cup size D
4in. more gives Cup size DD
5in. more gives Cup size E
and so on through F, FF and G
An example:
Underbust measurement of
29in. + 5in. = bra size 34
Overbust measurement of
34in. = Cup A
34E would measure 29/30 inch under bust and 39inch around fullest part
38C would be 33/34 inch under bust and 40inch around fullest part