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What is Sister Sizing?

The concept of 'sister sizing' seems simple, but is something many people know little about. Knowing how the concept works can be really helpful when trying on bras, allowing you to find the perfect fit. 

What is Sister Sizing?

Sister sizes are alternative bra sizes to your current bra size where the cup size stays the same even though the band size and cup letter change. Everyone has more than one size option when it comes to buying bras, these are called Sister Sizes, you can sister size up or down from your usual size to ensure you are getting a bra that fits comfortably. 

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How does sister sizing work?

Before discussing sister sizing, it is helpful to understand how bras are usually sized. This differs from country to country, but as a rule, cups sizes are represented by a letter (such as A, B or C) and band sizes by a number (32, 34 or 36). 

Band sizes and cup sizes are relative to one another, meaning a C cup, for example is not the same across band sizes. This is because the cup volume adjusts with the band size. For example, someone who is a 36C will have a noticeably fuller bust than someone who is a 30C, the capacity of a cup increases with the band size. 

Do I need to know my cup size to find my sister size?

Yes, Sister sizes are sizes that have the same cup capacity but a different band size. For example, someone who wears a 32C could also wear a 30D and a 34B depending on if they want a tighter or looser fitting bra. Make sure you have been fitted before finding out your sister size so you know which cup size you are.

Example: If you’ve been fitted and told that you’re a 34C and find that the cup provides good coverage with no gaping, but you find the overall fit a little tight on the back you may prefer a 36B. This gives you a looser, more comfy fit, but with the same cup volume as the 34C.


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If my size is sold out can I buy a different size?

Have you ever found something you love but your size is out of stock? Don't worry you might be able to shop another size. If your size isn't available you can try a size within your sister size range, sister sizes are a great tool if your normal size if sold out or a certain style isn't fitting right. If neither are fitting well it might be that the style isn't quite right for your shape.

Sister Sizing Chart:

Each pink line represents the same cup volume and Sister Size.


Should I Sister Size up or down?

  • Sister Size Down - If your bra is on the tightest hook then you might want to consider your Sister Size down. This is one band size smaller than your current band size and one cup size larger than your current Cup. For example, if you wear a 34C, your Sister Size down would be 32D.

  • Sister Size Up - If your bra is on the loosest hook and still feels a little tight then you might want to consider your sister size up. This is one band size larger than your current band size and one cup size smaller than your current Cup. For example, if you wear a 34C, your Sister Size UP would be 36B.

Remember, all brands and styles of bra will fit slightly differently, so it's a good idea to try a few different sizes to find what works best for you. The most important thing is that you feel comfortable.



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