Bra sister sizes explained: The size of a bra is unlike any other garment. Unlike other clothing, shoes, etc. for which a 6 is always smaller than a 12 a bra size depends on the ratio between two elements: the band and cup size. As a result, bras have multiple sizes that are compatible, and those alternate sizes will feature a cup bra sister sizesUse Sister Sizes to Find Your Bra Size | UpbraKnowing your bra's sister sizes can help you find your best fit when buying bras that run smaller or larger than normal. Its a common misconception that the larger the cup size, the larger the bra, no matter what the band size (i.e. a 32F is larger than a 36B, a 34C is larger than a 38A, etc). However, this is not the case. During the bra manufacturing process the same exact bra cup may be paired with different Sister sizes the magic trick of cup size | Miss Mary of bra sister sizesSister sizes when more than one bra size fits. This is what is called a sister size 38C is the sister of 36D and 40B. Lets say that you have size 38C. If the bra has an elastic back, you can probably also wear a 36D as it will stretch over time and adapt to your body.