June 25, 2019 4 min read

Are you looking for the perfect bra that fits you? Do you feel that finding it is difficult? Well, finding the right bra is quite different from finding the right clothes. And there is a lot of confusion when it comes to bra sizing. The right size is often not straightforward and many factors like your band size, cup size, and your particular breast shape contribute in matching a single bra size, which is a combination of unique number and letter.

If you have encountered the process of finding your right bra size as frustrating, then you have come to the right place. Here you can find an alternate and most effective hack which is the use of something called the ‘sister sizes’.

bra measurement, measuring

What are Sister Sizes?

Many women are unaware of the bra sister sizes. There is a lot of misconception prevailing among women that all cup sizes are usually equal in size, however, the reality is far from being different.

Sister sizes are the alternate bra size with equivalent cup volume but different band size and cup letter.  For instance, a bra of 38C and 30F are technically the same size as their cup volume are the same.

One needs to understand that cup size and band size are not independent entities, but they are more of interrelated one. They are like the ratio where one varies with others. Let us look upon it further. 

The Importance of Sister Sizes

You are not alone. Almost every woman has passed through the phase where they can't find the bra that fits their unique shape and size. Your sister size will come to your rescue when you are trying to fit in a bra that does not have your precise size of cup and band but are usually smaller or larger than your normal size.

If you cannot find your cup size in the size chart, you just need to increase the cup size and decrease the band size or vice versa to find a body fitting bra. Any changes in your body such as increase or decrease your weight needs many adaptations in your sizing also, as both band and bust sizes vary accordingly. During such circumstances, sister sizes come in handy.

It is totally a myth that if the cup size is larger, the bra should also be of larger size regardless of the band size. For example one may usually consider a bra of size 32F is larger than 36B or 34C is larger than the bra of size 38A. But this is quite far from reality.

The fact is that when bras are manufactured, multiple bra sizes are created which have exactly the same bra cup but varied band length. For example, the bra with 32D, 30DD, 34C, 36B, and 38A have the same cup volume.

The reason behind such a system is that as the band size within each letter increases, the size of the cup also increases slightly despite having no change in the letter mentioned. For example, the bra of size 34D and 36D will have a different length as well as different cup size.

Once sister sizes are understood, you will easily solve all the issues regarding the bra fitting.

How to measure your sister size

So the important question is how to measure the Sister Size. There are two techniques to find your best sister size.

1. Sister Up

The sister-sizing up means increasing your band size and parallelly decrease the cup size according to it. This Sizing up comes to your help when your band is too tight and the bra is almost fitting you. It allows giving a bigger band size while maintaining the same cup size. Although the cup may slightly feel shallow to you, it will not affect your fitting to a large extent.

For example, the sister sizing up of the bra size 34C will be 36B.

sister size up and down

2. Sister Down

This is the opposite of Sister Up process. Here we go down on the band size and size up on the cup size. This technique is used when cup size and wire fitting is almost comfortable but the band is loose. With Sizing down, one will get a smaller band while maintaining the same cup volume and a similar fit. The cup may now feel slightly deeper.

For example, the sister sizing down of the bra size 34C will be 32D.

Below shown chart comes to your aid where you can find your current size of bra and the sister size for that is mentioned in the same row accordingly. Each row listed below is the family of sister sizes.

current size and the sister size bra chart

So ladies, armed with this knowledge, you can easily find the right bra size. With the help of bra sister size, you will have a comfortable band fit and the perfect cups that will fit you like a dream!

Want to know how to measure yourself well? Check out our helpful guide here. And once you have found the right size and sister size for yourself, take a look at our collection of super comfortable maternity nursing bras here. Go show yourself some love, ladies!

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