짧게 요약하면 다음과 같습니다.

BAND SIZE : 밑가슴 둘레를 인치로 잰 후 5를 더합니다.
CUP SIZE : 유두위로 가슴둘레를 인치로 잰 후 band size를 빼면 컵 사이즈가 됩니다. 1인치 이하 AA, 1인치 A, 2인치 B, 3인치 C, 4인치 D, 5인치 DD

원문입니다.

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 29" + (5) = 34" band size.)


CUP SIZE : Measure completely around the bust at the fullest point.
• Each inch of difference between this measurement and your BAND size = cup size. (i.e.: If your band size is 34" and your bust measurement is 35", you wear an "A" cup.)


If the difference is:
less than 1 inch = AA cup 3 inches = C cup
1 inch = A cup 4 inches = D cup
2 inches = B cup 5 inches = DD cup