Bra sister sizes | Do sister sizes really work?

two women sitting plus size lingerie

If you know about bra sister sizes, you’ll know everything you need to know about bra sizing. Learn about your alternative sizes in this short guide.

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What are bra sister sizes?

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If your bra is hurting you, it’s sure time to check upon your sizes and finding out your sister size.

Every bra size is surrounded by a set of bra sister sizes. Although these sister sizes have different band sizes and cup numbers, the cup volume of the sister size is the same.

  • We all have a sister size we could wear. For example, the bras 40C and 38D have the same cup volume and might fit the same woman.
  • Especially if you’re in between two possible sizes (most women are in between sizes)
  • If you know the alternative sizes you can choose from, it makes shopping so much easier.
  • Bra brands may have a different fit and you might need to go down or up with the band and cup size.

I myself have 3 different bra sizes that fit me just fine. I have one bra size I wear the most. Sometimes I go for a band size 36 instead of the 34 I usually wear. In this case, I go down a cup size to keep the same cup volume.

The cups in a 36 are also a bit wider set and I find this sometimes better for me. Depending on the brand and bra style I try different sizes and actually own different sizes.

woman holding measuring tape

When measuring your band size, hold the tape firmly around your body. Measuring your bust size should be done over the fullest part of your busts

Herroom has a great video on how to measure your breast size See video Herroom here


Going up a band size – want to keep the same cup size

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You wear a 36C bra and are not happy with the band size finding it a bit too tight. You don’t wanna change the cup size.

  • you choose bra size 38B (that is your bra sister size).
bra sister sizing example
A 36C and a 38B have the same cup volume


Going down a band size – want to keep the same cup size

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You wear a 36C bra and are not happy with the band size finding it a bit too loose. You don’t wanna change the cup size.

  • you choose bra size 34D (that is your bra sister size)
A 36C and a 34D have the same cup volume

If you want to change your band size but not your cup size you will have to know what to choose. Because when going up or down a band size, the cup size of the bra will have to change too in order to keep the same cup volume.

Check your sizes in my bra calculator

Knowing your bra sister sizes will give you more control when shopping for a bra. Depending on the bra style and the bra brand, you’ll know what sizes you can try.


Other articles you might like

How to measure bust size correctly
Why is my bra hurting?
Bra conversion chart EU – US
Is my cup size too small?
The bra size calculator


Thirdlove Fit Finder

photo of models showing bras from the thirdlove collection

Find My Fit »


Herroom Bra Video Tutorials


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