BAND SIZE
Measure around your ribcage, directly under the bust.
Add +5 to this measurement to obtain your band size. (i.e.: If your ribcage measurement is 30" + (5) = 35" band size.)

CUP SIZE
Measure completely around the bust at the fullest point.
Each inch of difference between this measurement and your BAND size equalls the cup size. (i.e.: If your band size is 35" and your bust measurement is 37", you wear an "B" cup.)

IF THE DIFFERENCE IS:
Less than 1 inch = AA cup
1 inch = A cup
2 inches = B cup
3 inches = C cup
4 inches = D cup
5 inches = DD cup