Bra sizes 38A and 32DD actually hold the same volume of breast tissue. This is due to our favorite bra-shopping hack called sister sizing. What is sister sizing? Remember that a bra cup size is always relative to its band size, calculated as the difference between the bust circumference and the torso circumference. Therefore, as the band size bra sister sizesSister Sizes: Why Every Woman Should Know for Bra Fitting bra sister sizesBra Sister Size Chart. Below is a sister size chart from which you can find bra sizes that is related to your actual size. You should start with the size for which you have been measured, and the size that you are looking for in the lingerie shop. Moving along the same row, you will find the sister sizes that have the same cup volume.Sister Sizes: The Bra Secret Every Woman Should Know bra sister sizesMay 14, 2019 · Sister sizes are groups of bra-size equivalents that are related by cup volume. For example, a 36F (DDD) cup belongs to the same family as a 38E, a 40D, and a 42C. Stick with us well explain. But just know that your perfect fit may still be out there waiting for you.