underwire bras

Purchase several bras of different brands that offer a good fit. Measure around the fullest part of your chest.

Using a fabric tape measure, find the distance around your rib cage. Adding five to this number gives you your correct bra size.

Subtract your first number (ribs) from this new number. The difference between the two gives you a cup size. One inch is equal to a full cup size, so 1=A, 2=B, etc.