Take measurements of your bust by measuring around the fullest part of the chest. 2. Take the under-bust measurement by measuring just under the bust line. 3. Subtract the full-bust measurement from the under-bust measurement. 4. The difference in inches corresponds to a cup Size as seems below: 1″ = A 2″ = B 3″ = C 4″ = D 5″ = DD 6″ = DDD 7″ = G 8″ = H