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  4. Every bra size has a sister size: This is how it works

Every bra size has a sister size: This is how it works

Why is it important to know your sister sizes?

We don't have to tell you why it's so important to know your bra size. Comfort, posture, confidence: The right size and style can work wonders for them all. Getting professionally measured in a lingerie boutique (or taking your own measurements) is a must. Once you know your bra size, it’s useful to figure out your sister sizes as well. This can come in handy when trying on lingerie. If your size is no longer available or if the cups or the band are too big or too small, try one of your sister sizes.

Sister sizes: A system for small and large sizes

Sister sizes are easy to figure out and are the same regardless of your cup size. Start with your own bra size, which consists of a band size (the number) and a cup size (the letter). Your cup size is calculated in relation to your band size. Cup size doesn't express volume, but the difference between the measurement just under the bust and the measurement around the fullest part of your bust. This explains why someone with a 75D may have smaller breasts than someone with a 90C.

To determine your sister sizes refer to the size chart, where they are expressed in a diagonal line. If you go up a band size, go down a cup size. If you go up a cup size, go down a band size. For example, if you're an 85C, your sister sizes are 80D and 90B. Remember to always use the same size system, as the EU system differs from the French and US systems.

Are sister sizes always a good alternative?

If your bra size feels looser or tighter than usual in a new brand or a new style, it’s worth giving your sister sizes a try.

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If your favorite bra is no longer available in your size, a sister size can be a great solution, assuming it fits well and offers the support you need. If you have to fasten the bra on the tightest hook in your usual size for a snug fit, your sister size (one band size up and one cup size down) may be too big for you. To make sure your fuller breasts get the support they need, it's important to make sure the band fits snugly around your body. After all, it's the band – not the cups – that provides the majority of the support.

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