What is a sister size in a bra?

Bra sizing works by taking both cup and band into account. This results in a vast and varied range of bra sizes that can accommodate a broad scope of unique bodies. This also means that the differences between certain sizes can be quite slight and subtle.

A sister size is when you go up in band size and down in cup size, or up in cup size and down in band size. These similarly sized bras are known as sister sizes.