Measure around your rib cage right under your breasts. The measuring tape should be snug but not too tight.
Round to the nearest whole number. If the number is even, add 4". If it’s odd, add 5". Your band size is the sum of this calculation.
(For example you measured 32", your band size is 36. If you measured 33", your band size is 38.)
Measure the fullest part around your breasts. Do not pull the measuring tape tight.
Subtract the band size from your bust size.
The difference will help determine your cup size.