Measurements are a good starting point for establishing a well-fitting bra, but remember that sizes may vary from brand to brand and style to style in a given brand.
The following charts are a guideline for establishing your average fitting when being fitted for a new bra.Find your band size
Measurements should be taken while wearing a bra. The measuring tape should be held snug but not tight while measuring. Begin by measuring around the ribcage directly underneath the bust. If the measurement is even add 4" and if it is odd add 5" to result in a whole number for the band size. For example if you measure 30" add 4" you band size will be USA 34 = AUS 12. If you measure 31" add 5" and your band size would be USA 36 = AUS 14.
International Band Sizes
Find your cup size
Take your second measure around the high point or fullest point of the bustline while wearing a bra. Subtract the under-bust size from this size. For example; if you measured 39" around the bust minus 36" around the under-bust equals 3" difference or cup size C.
Underpants sizing chart