MEASURE YOUR BAND OR (CHEST) SIZE- This is the area under the bust where the band of your bra usually sits.
ROUND TO THE NEAREST NUMBER- If your measurement is even then add 4 inches to the band size. If your measurement is odd then add 5 inches to the band size. For example band size is 32 add 4 inches and total band size is 36. Or band size is 31 add 5 inches and band size is 36
BUST SIZE- Measure the fullest part of your bust (breast area). Use actual numbers here.
DETERMINE CUP SIZE- Your accurate bust size is going to be an equation of your bust size (minus) - your band size = your cup size. The following are the cup sizes: 0=AA, 1=A, 2=B, 3=C, 4=D, 5=DD
For example: bust 36inches - band size 34 inches you are a B cup