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what are bra sister sizes

Hopefully, you know your bra size. In fact, you may have even sought out a professional for a fitting to make absolutely certain you have it right (well done, smart move!). But do you know your sister size? If not, consider this: It can be equally helpful when lingerie shopping. The fact of the matter is that bras are incredibly complex garments when it comes to the construction and fit. That’s why, as you’ve likely noticed, different brands and styles of bras may fit you differently despite having the same cup letter and band number on the tag.

Fortunately, sister sizes can help solve some of those problems. Ready to make bra shopping a whole lot easier? Follow this guide to fully take advantage of this helpful little system.

Bra sister sizes explained:

The size of a bra is unlike any other garment. Unlike other clothing, shoes, etc. —  for which a 6 is always smaller than a 12 — a bra size depends on the ratio between two elements: the band and cup size. As a result, bras have multiple sizes that are compatible, and those alternate sizes will feature a cup volume that’s very close to your regular bra size, but with the next band size either up or down.

Why they’re helpful:

Sister sizes can come in handy for several reasons. For one, when you’re trying on a bra that doesn’t run totally true to size, you may find that your sister size offers a flawless fit. If there’s a little too much room in the band but the cups fit well, you can go down a band size and up a cup size.

Conversely, if the band feels too tight, you can go up in the band size and down in the cup size. Additionally, if you find the cups gaping on a particular bra because you’re not totally filling them out, you can size down in the cup and up in the band. Or, if the cups are squashing down or cutting into your bust (no one likes a quad-boob), you can benefit from going up a cup size and down a band size.

You may have found that different styles of bras differ slightly in terms of sizing. An unlined wire bra could potentially fit you differently than a padded plunge bra, for example, depending on your breast shape. This is another way in which sister sizes can prove helpful. By knowing your compatible sizes, you can find your perfect fit in any style.

Have you ever experienced the devastating feeling of finding a bra you adore… that isn’t available in your size? Maybe the brand simply doesn’t make your size, or maybe they’re sold out — either way, it’s undoubtedly a bummer when you realize the lingerie of your dreams is suddenly out of reach. Luckily, you may be able to solve that problem if you know your sister sizes.

Related: Bra Fitting 101: Band Sizes, Cup Sizes, and Sister Sizing

How to find your bra sister size:

OK, so by now you’re well aware of all the perks of knowing your sister sizes. Now the question is, how do you figure out yours?

Put simply, it’s a matter of opting up one band size and down one cup size, and vice versa. For example, if you normally wear a 36E, your sister sizes would be 34F and 38DD.

Since it’s a complex matter, though, you may want to turn to this simple chart to take the hassle out of figuring it out. This particular chart also features UK to US cup size conversions as well to make things even easier. All you have to do is find your regular bra size, and look for the sizes listed directly above and below it (the one above will have a smaller band and larger cup, while the one below will have a larger band and smaller cup).

Other helpful tips:

First thing’s first: It’s crucial to know your true bra size before figuring out your sister size — this ensures that you achieve a flawless fit, no matter what. That’s why we advise periodically getting a professional fitting.

Once you know your actual size, it’ll be a whole lot easier to find its sister. Keep in mind that a vast majority of a bra’s support lies in the band, so it’s imperative that you have the right band size to begin with before going up or down in that measurement.

Are you currently hooking your bra on the tightest hook-and-eye closure? Then you’ll likely find that a sister size with a larger band is too loose.  On the other hand, if you’re fastening your bra on the loosest possible hook, a sister size with a smaller band could dig into your torso, proving quite uncomfortable.

Since sister sizes aren’t always an exact science, it’s a good idea to try them on before buying them — or at the very least, check out the size charts for that brand and read any product reviews (when available) to determine if a particular style runs small or large.

Now, aren’t you glad you know what all the hype is about? Sister sizes can make bra shopping a lot simpler by enabling you to find the best possible fit in any brand or style. So what are you waiting for? Once you’ve figured out your own alternative sizes, you can use that knowledge to snag some lust-worthy new lingerie for your collection.

Related: Find Your Bra Sister Size With Our Simple Chart

We Highly Recommend

Whether you’re shopping for new everyday bras or lingerie for a special occasion, it’s always a good idea to seek out a second opinion. We know how hard it is to find bras that fit well and feel good, especially when you’re doing it on your own. If you’ve ever felt unsure about your bra size or you just don’t know where to go to find good bras, it’s time to let a bra fitter help.

Many specialty lingerie boutiques offer bra fittings. Their expert bra fitters will take the pain and frustration out of bra shopping and do all the work for you. Even better, their product knowledge can save you time and money. Plus, they know where all of the best bras are hiding.

If you’ve struggled with finding bras in the right size, it’s time to make a change. Visit our specialty store locator to find a store near you and schedule an appointment.

Happy bra shopping!

Featured image lingerie:
Parfait Jeanie Plunge Molded Bra 4801 in Panther Print, Java, Navy Blue
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Published by

Rebecca Strong

Rebecca is a Boston-based freelance writer who focuses on style, fitness, food, and travel. She has contributed to such publications as HuffPost, Elite Daily and U.S. News & World Report. When she's not writing, she can be found at home or in the studio working on the songs for her upcoming album. Her favorite bra is a black demi-cup style with all-over-lace — timeless and feminine.

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