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Bra sister sizing and other fit concepts unveiled

Bra sister sizing, band measurements, cup volume… what does it all mean?

When it comes to finding the perfect-fitting bra, navigating the world of sizes can be an intimidating task. The United Kingdom has its own unique system for sizing bras, with band size, cup volume, and the concept of bra sister sizing playing crucial roles.

In this article, we will dive deep into the intricacies of how bras are sized in the UK, unravel the mystery of band size and cup volume, and shed light on the concept of bra sister sizing.

Understanding Band Size and Cup Volume

The foundation of a well-fitting bra lies in understanding the two fundamental elements of sizing: band size and cup volume. In the UK, bras are sized using a combination of numbers and letters, such as 32B or 38DD. Let’s break down these components:

1. Band Size:

The band size corresponds to the measurement of your underbust. It is represented by the number in your bra size (32, 34, 36). This number indicates the circumference of your ribcage just below the bust. A snug but comfortable fit is essential for proper support.

2. Cup Volume:

The cup size, denoted by letters (A, B, C, D, etc.), represents the difference between your bust measurement and your band size. It signifies the volume of breast tissue the cup can accommodate. Each increase in cup size signifies an increase in breast volume.

bra sister sizing
Bra Sister Sizing- unveiling the concept

Bra sister sizing is a revolutionary concept that allows you to find your ideal fit even when the perfect size isn’t readily available. It involves finding bras with different band and cup sizes that maintain the same cup volume. This means that if your usual size is unavailable, you can opt for a sister size that provides a comparable fit.

For instance, if you typically wear a 34C, your sister sizes would be 32D and 36B. While the band size changes, the cup volume remains the same. It’s important to note that the fit may not be identical across sister sizes, but they can offer a comfortable alternative when needed.

The Beauty of Bra Sister Sizing

Bra sister sizing allows for flexibility and adaptability, especially when shopping for bras from various brands or when sizes are limited. It’s a handy tool for those who fall between standard sizes or experience minor fluctuations in weight or body shape.

The key to successful bra sister sizing lies in understanding your original size and how it relates to neighboring sizes.

have a look at our bra sister sizes chart below. Simply find your usual bra size and the other sizes along the row are your cup volume sister sizes. Usually you would only go up or down one back size. 

bra sister sizes chart
Bra sister sizes chart: Find your usual size, along the row are your sister sizes which should provide the same cup volume
Tips for Finding Your Perfect Bra Size

1. Check how your current bras are fitting: The first step in finding your accurate bra size is to check your bra fit using our fitting guide. This will provide you with a starting point for your bra shopping journey. If you really have no idea- book in for an online fitting with us.

2. Experiment with Sister Sizes: If what you think is your ideal size isn’t available, consider trying on sister sizes to determine which one offers the best fit. Remember that band size affects comfort and support, while cup volume impacts the fit around your breasts.

3. Account for Brand Variations: Sizing can vary significantly between brands and styles. That is why we include our Locker review with all our bras, so you can see how all the different bras fit on one standard tester.


Bra sizing in the UK involves a combination of band size and cup volume, with the concept of sister sizing providing a versatile approach to finding the perfect fit.

Armed with the knowledge of your measurements and the principles of sister sizing, you’ll be equipped to navigate the world of bras with confidence. Remember that comfort and support are paramount, and a well-fitting bra can make a world of difference in how you feel and carry yourself.