What Are Sister Sizes?

DEC. 16, 2021

What are sister sizes?

When two bras have sister sizes, it means they share the same amount of the volume in the bra cups, but different band lengths.

Understance What are sister sizes. for bras

How do sister sizes work?

There are two components of a bra size: the BAND SIZE, and the CUP SIZE.

BAND SIZE corresponds to how wide your ribcage is.

CUP SIZE corresponds to how much volume your breasts have.

When two bras have sister sizes, it means they share the same amount of the volume in the bra cups, but different band lengths.

For example, 36C and 38B are sister sizes. Their cups are made for the same breast volume. Only, the 36C has a shorter bra underband from the 38B.

Can you wear them interchangeably?

Only if you are kind of in-between band sizes. If you are between 36 and 38 in band size, you can probably make both 36C and 38B work.

However, if you are on the smaller side of 36C (for band size), the sister size that could work for you is 34D. On the other hand, if you are on the bigger side of 38B (for band size), the sister size that could work for you is 40A.

So, does that mean 34D and 40A are sister sizes? Absolutely not. We do not recommend wearing a sister size that’s more than one “sister” off. 36C and 38B are ok. 36C and 40A are not. The band length difference is too much – a 36 band is likely going to be too tight for someone who usually wears 40, even if you are on the smaller side of 40.