Feb 20, 2017 · Sister Sizing is the name that the lingerie and bra fitting industry use to discuss similar bra sizes with different bra band sizes. They are related, if you will. Usually, calculating your sister size is the result of changing the band size, which then affects the cup size.Bra sister sizes | You too have a bra sister size | learn bra sister sizesSister sizes have the same cup volume even though their cup size and band size both have different numbers. For example, the sister sizes of a 36B bra are 34C and 38A. Why you wanna know your bra sister sizes? Knowing about sister sizes makes it easy for you to choose an alternative size if Bra Size Chart ThirdLoveJul 02, 2020 · Bra sizes that share a row are called sister sizes, meaning they share the same cup volume (though they have different cup letters). For example, the row with bra sizes 36C, 38B, and 40A all have the same cup volume, but have different band sizes. The same goes for the row with bra sizes 38H, 40G, 42F, 44E, 46D, and 48C.