Bra Size Unavailable? Sister Cup Size To The Rescue! December 04 2019

What Are Sister Sizes?

If finding your right bra size is a frustrating process, there are some sizing hacks that can help and remember: it’s not you, it’s your bra.  

One of the most effective of these is the use of “Sister Sizes”.

You may be unaware that every bra size has several "Bra Sister Sizes"- these are sizes where the cup volume stays the same even though the band size and cup letter change.

It’s 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 band lengths to create multiple bra sizes. For example, the same exact cup is used to make 38A, 36B, 34C, 32D, AND 32DD bras! 

Knowing your bra's sister sizes can help you find your best fit when buying bras that run smaller or larger than normal.

How to Find Your Sister Size

  • Go up a band size (if your band is too tight), but go down a cup size.
  • The same rule applies in the reverse if your band is too loose: go down a band size, but go up a cup size.
We promise it only sounds more complicated than it is, so we created a handy sister size chart for you.


Find your current bra size, and your sister sizes are the ones listed in the same row (going across). So, for example, if you’re a 12/34F (like me), your sister sizes are 8/30H, 10/32G, 14/36E, 16/38DD, 18/40D, 20/42C and 22/44B. Each row is a family of sister sizes.

I've tried most of my sister sizes with some fitting better than others so use them as a guide and you might be as surprised as I was to find the 18/40D fit well!

PS your band size is NOT related to your body size.