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Bra Sister Size : What You Need To Make Bra Shopping Easier

Bra Sister Sizes

Has anyone ever mentioned sister sizes to you and you never understand what it means, when to use it or how to use it?

Below are the answers to make your bra shopping a lot easier for you.

So, what is sister sizing?

Sister sizing basically refers to the same cup size but on a different size band. As a bra band size gets smaller, the same cup volume will have a bigger letter, and vice versa. For example, if you wanted to buy a 32D and it wasn’t available in the shop, you can also look for a 30DD or 34C which equates to you wearing the same cup size but just on a different band.

Essentially the D cup size on a 32 band is the same size in a 30DD and 34C…all you are doing in adjusting the band size.

Hope you are following me so far :)

Sister sizes

When should you use sister sizing?

Usually sister sizing is used if your bra size is not available so you look for the equivalent in another band size. Sometimes when doing fittings, I have used sister sizing when customers have lost some weight but their cup size hasn’t gone down. An example is a customer being a 36F when I first measured them and they lost a bit of weight between their next fitting. Her back size was smaller so I moved her to a 34FF bra which accommodates the weight loss but the cup size stays the same to provide support for her bust. This just helps to make the bra fit a bit better without compromising on the support.

How does sister sizing work?

Imagine your bra size is currently a 32G – so the two basic rules are:

· If you go up a band size, you need to go down a cup size


· If you go down a band size, you need to go up a cup size

Are you with me so far?

So, going back to your imaginary bra size, if you are a 32G and a shop doesn’t have it in stock you can either look for a 34FF (going up a band size and going down on the cup size) OR look for a 30GG (going down a band size so you go up a cup size)

I have also included a table below to visualize what size sister looks like for different bra sizes

Original Size Sister Size with Smaller Band Sister Size with Larger Band
32D 30DD 34C
34F 32FF 36E
38G 36GG  40FF
40H 38HH 42GG

Looking at the table – a 40H has the same cup size as a 38HH or 42GG. All you have done is adjusted the band size.

What should I look out for when using sister sizing?

Approach sister sizing with caution – although the cup size volume doesn’t change with sister sizing, you are changing the band size so you need to ensure that the band size you choose still provides the right support as from research, 80% of your bra support comes from the band.

One example: I wanted the Lepel Fiore navy bra but they only have it up to a G cup and naturally I am a 30H. So, I thought, I’ll just get the sister size to a 30H. As I was going down two cup sizes for me to be able to get the G cup – I had to go up two band sizes (30H = 32GG = 34G) I ordered the 34G in the navy Fiore and was so disappointed as when I tried it on, the band was too big for me so the bra just didn’t provide the support it needed. The band wasn’t snug so it was riding up my back which essentially made my boobs drop down.

Also be careful when switching between brands as their measurements are slightly different to others i.e. Charnos cup sizes are a bit more generous than brands like Freya and Curvy Kate.

So be careful – a tip is to not go too far into sister sizing. My advice? Just stick to using sister sizing when necessary and just use it to go up or down by one band size to make sure to don’t compromise the support the band gives you.

Sister Sizing

What’s next?

Next blog, we are talking band sizes and why they are so important – the correct band size is the gateway to you enjoying wearing bras and sometimes even forgetting that they are there with all that comfort!

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