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They Don’t Have Your Bra Size? Try Your Sister Size for a Great Fit

These alternate sizes might even fit you better.


Picture it: You finally decide to surrender Ol’ Reliable — the now-stretched, warped, and threadbare bra that once was your favorite. It was the perfect bra when you got it (more than a few years ago) but it’s time to put it to rest and find a bra that works better for you. You go to the store where you found it before, excited to purchase a refresh, but — oh no! There aren’t any bras in your size available. What are you supposed to do? Before you give up, consider trying out your sister size — an alternate size that might even fit you better. Read on to learn more about sister sizing and how to find yours.

Bra Sizing Explained

Before you determine what other sizes work for you, it’s good to know how sizing works. Bra website SheScience explains that the number associated with your size (32, 34, 36, etc.), your band size, represents the width of your ribcage — not your shoulder width, as some believe. The letter of your bra size (A, B, C, etc.), your cup size, represents the volume of breast tissue. It is not, by itself, a unit of measurement, but is instead dependent on your band size. For example, as SheScience notes, a 32B sized bra and a 38B sized bra do not have the same cup sizes; in fact, the 38B is four cup sizes larger. For each increase in band size, there is an increase in cup size, and vice versa. Who knew bra sizing was such a science?

What are sister sizes?

Because cup sizes are dependent on the bands, you have a lot more flexibility in bra sizing than you may think. Bra site Finally Bra defines your sister sizes as “a group of sizes that provide the same cup volume.” It’s important to know your sister sizes for multiple reasons. When you go to the lingerie store for a new bra, for example, your usual size might be out of stock — so it should be a relief to know there are a variety of sizes that might work instead. Also, you might get a better fit with the slight differences in band and cup sizing that sister sizes provide. If you’ve ever been in the fitting room trying on your usual size and thinking, wow, this is almost perfect —  if only the band was just a tiny bit looser… or if you’re bothered by ever-so-slight but noticeable gapping in your cup sizes, your sister sizes might be the solution to your problem.

How do I find my sister sizes?

There are multiple ways to find your sister sizes. Finally Bra shares that you can either go up in band size and down in cup size or go down in band size and up in cup size. For example, if you are normally a size 34C, your sister sizes are 30D, 34B, and 36A. As you can see, for each increase or decrease in band size, the cup decreases or increases proportionately. See the chart below from bra website Amanté for help finding your sister sizes. 

bra sister sizing chart
Courtesy of Amanté Lingerie

Important Things to Know About Sister Sizing

Once you play with the band and cup ratios, you’ll soon find that you have a large selection of sister sizes from which to choose. If you’re looking for the best fit possible, there are a few things to keep in mind. 

To size up or size down: Because you can go up or down in the band or the cup, finding the right sister size can feel overwhelming. Lingerie website Fleur of England offers some clarity: If your band feels a little loose on the tightest hook of your normal size, try going down a band size and up a cup size (example: from 34C to 32D). Conversely, if your band feels tight on the loosest hook of your normal band size, try going up a band size and down a cup size (example: from 34C to 36B). 

Consider your current bra: When using your normal, everyday bra as a point of reference for sizing, keep in mind how long you’ve been wearing it. Regardless of size, your bra loosens, stretches, and changes shape as time goes by, says Fleur of England. If you’re trying sizes on in a store, it might be a  good idea to bring a fresh bra of your current size into the dressing room for a more accurate reference. 

How to know when it fits: Because there are so many sizes that might fit, how do you know when one is the perfect fit? Bra expert Kimmay Caldwell says that the most important thing to look for in a bra is a snug-fitting band. If it isn’t snug or doesn’t feel quite right, don’t settle — try on another size. And just because there several sizes you can choose from doesn’t mean they’re all the right size, or even the same size. Sister sizes aren’t identical. “Keep in mind how actual sisters are,” says Caldwell. “They may be similar, but they are not ‘the same.’”

Trying on bras can be a daunting task. That’s why it’s such a relief when you find one that works for you. When you’re looking for a better fit, keep in mind that your options are not as limited as you might have thought. The right bra can give you confidence — so, go out and find the perfect one. You deserve it!

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