Posted on by Olivia Pauline

A bra sister size? What exactly is that? Fret not, for you are not the only one asking that question. A lot of women actually have no idea what “bra sister sizes” are.

Bra sister sizes are the answer to the seemingly endless problem of finding the right bra size and fit. A sister size is called such because it is related to your bra size and has the same cup volume. Bra shops and department stores have sister sizes that women can try out when their actual size does not fit for some reason. Or perhaps, the bra you really want to buy is out of stock in your preferred size. In this case, it's helpful to know your bra sister size.

Since the cup size depends on the band size, it is understandable to adjust both when your actual bra size does not fit you. Every bra size has 2 possible sister sizes. To determine your bra sister size, move your current "number" (band size) and "letter" (cup size) by one unit in opposite directions. For example, if you're a 34C, your sister sizes would be a 36B or a 32D.

A bra sister size table or chart would definitely make this conversion easier.

Bra Sister Size Conversion Table 

Measuring Your Bra Size

If you're unsure about your actual bra size in the first place, it'd be helpful to determine it, and then get your 2 sister sizes thereafter. A simple measuring tape is all you need.

The first step is to get your band size. To do so, you need to get the measuring tape as parallel with the ground as possible. Place the tape around your bra, under your bust. Be sure to let out the air from your lungs when doing so as this will help you get the best measurement.

Step number two involves measuring the cup size. Stand straight and place your arms on your side. Look for the fullest part of your breast and place the measuring tape there. Be sure that the bra you’re wearing is not padded. Additionally, the measuring tape should be parallel with the ground, similar with what you did when you measured your band size.

Here's a quick diagram showing you to determine your true bra size.

How to determine your bra size

Your measurements should be rounded to the nearest whole number.

To determine your sister sizes, you need to remember only a couple of things. First, if the band size increases, the cup volume decreases. Second, if the band size decreases, the cup volume increases. This is why there are sister sizes. Basically, your breast can fit into more cup sizes than you know.

Bralettes typically encompass a range of 3 bra sister sizes, since they're designed to be looser-fitting without much support or push up.

Bralettes like this Miranda black lace bralet encompass a range of 3 bra sister sizes

If you want to explore your sister sizes, you simply need to go online and look for a chart that lists all the bra sizes and their substitute sizes. Bra shops should have sales personnel who are knowledgeable about sister sizes, too.

Although sister sizes are not guaranteed to work for all women, as we have different bust contours and body build, they are guaranteed to offer a more convenient and practical alternative to many. If you know your sister sizes, for example, you won’t need to spend hours inside a bra shop trying on one bra after another until you find the one that fits you perfectly. You won’t have to go bra shop hopping just to find the ideal bra size. You’ll save a lot of time, money, and effort. 

When you’re sure you cannot fit into your actual size, consider sister sizes. Better yet, when buying a bra, try on both your actual size and sister sizes, because sizing varies between brands, especially if they come from different countries. Basically, wearing your bra sister size is like wearing your boyfriend or husband’s extra small shirt in place of your large-sized shirt.

Remember, if you’re not comfortable with the bra you’re wearing, you won’t feel and look good in it. So, it’s important to consider sister sizing if you cannot find the right fit for you.