Suffering the woes of an odd bra size is a complete bummer (those of us with narrow torsos and large breasts). But on the other hand, having a common correct bra size can be frustrating, too. It seems as though department stores never carry your size, or there’s so many other people wearing the same size as you, there’s never a bra left! There’s a quick fix that women have have been using to get by and find a bra that works, even if their correct size is unavailable. The method of bra hunting they are using starts with the idea of sister sizing. Before we get into sister sizing, let’s have a brief refresher on how bra sizing works in general.

Sizing Review

Bra sizing works on a sliding scale. The cup size and the band size mean almost nothing without the other. It would be like giving an answer to a math problem and not giving your units as a part of the numerical answer. Bra sizing (in the US) works by taking the circumference of your chest and your bust, and taking the difference between the two. The difference in inches is then counted down the alphabet from A.

The letter you come to in conjunction with your smaller chest circumference is you true bra size. If you like a more loose fitting bra, you could always modify you size by going down a cup size (closer to A) and up a band size (larger number). While most people think that all D cups hold the same volume and the cup is just added on to your size, that’s not true at all.

This should give you a little more room if you don’t like overly snug garments. An example: Chest circumference of 32, and bust circumference of 40. The difference between these two is 8 inches. Thus, we would count to an H cup (32H). If we find this bra is a little tighter than we like, we can go to G, and to a band 34. This modification of your size is called a sister size. Let’s talk a little more in depth about what sister sizes are.

Sister Sizes

As mentioned previously a 32H and a 34G are sister sizes, and are relatively the same bra. Understand, these bras are not identical. Sister sizing is helpful if you are in a desperate pinch, or if you find your true size isn’t your favorite fit. As I stated above, some of us like tighter garments, others like a more loose fit while still maintaining support. This is why sister sizing can be great.

Take this example of 34DDD sister sizes: in theory, it’s possible to wear a 32F (or 32G, depending on the country), or to go up to a 36DD. In fact, a few of my friends who wore 36D bras for years realized after a proper bra fitting with me that they were actually 32DDDs.

So what makes these sizes different if they’re kinda interchangeable? It how the bra fits the individual really. In theory, the sister sized bras will hold the same volume of your breasts, but the band will fit differently. If drawn on a diagram, you may notice that the further (larger or smaller cup) you get from your “true” size, the farther apart or closer together the cups become.

Sister Sizes can be convenient if you have wide set breasts, you can try troubleshooting cup spillage around the armpit by using a sister size with wider set cups. On the same note, if you find your breasts are more compact, round, and stick out from your body, and your bras are proportioned wrong, try a sister size. Same goes for women who have more round breasts, that are flatter against their body. Go up a cup and down a band size. This should make the cup larger in diameter, and more accommodating for your breasts.

First example: Your true size is 34D, you could go up in band size and down in cup size for a 36C, or the opposite and come to a 32DD (32E).

Second example: If your true size is 38B, sizing up the band would get you to a 40A, or the opposite for a 36C.

Third example: If your true size is 32F, your two sister sizes would be 34E (34DD) and 30G (30DDDD).

But beware, as you get into the larger cups sizes, things can get a little more difficult. Of course!

Sister Sizing for DD+

It is recommended that you only utilize sister sizes that are within one cup size (up or down) of your true size. This is because bra manufacturers have anticipated different body types in these sister sizes. As the cup size goes up and the band size goes down, you will find bras proportioned with more projected cups and narrow bands for holding the breasts. Alternatively, if the cup size goes down and the band goes up, you will find bras shaped more shallowly and with a wider band.

If you’re finding your two sister sizes aren’t exactly working out. That’s completely normal. They aren’t your true size, so they won’t be the best fit bra you wear. However, if you think they’re really off, you should keep in mind the following tip. If you find you’re spilling over the bra, but the band fits perfectly, go up a cup size (or the opposite for under filling a cup). If the band is wrong, but the cups are perfect, try adjusting to a larger or smaller band on the same cup size. Of course, the unique shape of your breasts may make this process much more difficult than  I’m making it seem. But hang in there and be patient.

What I would ultimately recommend for anyone with DD+ breasts (in your “true” size), avoid sister sizes if at all possible. Like I said earlier, if you are in a pinch and have to go braless or choose a sister size, maybe that okay. But otherwise, you may be setting yourself up for discomfort.

Quick Refresher on Sizing and Fitting

So, worst case scenario is you’ve been at the store trying bras on for the last hour with absolutely no luck. Bands and cups around your true bra size are all over the place and nothing fits. Let’s ask a simple question: Are you 100% sure your “true” size is actually correct? When was the last time you were fitted for a bra? Were you ever fitted professionally? Our breasts change size, shape, and firmness over time, causing changes in our sizes. In addition to this, as many as 95% of women are wearing the wrong bra size. Isn’t that insane? Here are a couple quick tips to making sure your true size is actually your true size.

  1. The band should be firm and snug around your body, but comfortable to wear. Standing side-on at a mirror, the band should be horizontal and should not be creeping or pulling up your back.
  2. There should be absolutely no poking, rubbing, or digging anywhere. The underwire at the front should lie flat against your rib cage. If they stick up or out funny, they’re the wrong shape for your body and breasts.
  3. Each cup should completely encompass each breast. There should be a smooth line where the breast and the top of the cup meet. Even if you are wearing a low cut style or balconette, there should be no ridge or spillage over the top of the cup.

Understand that wearing the incorrect size and shape bra for your body can not only be unflattering, but it can be damaging you, both emotionally and physically. Ill fitting bras can cause back and shoulder pain, leading to poor posture and spine issues. You could face chafing and painful rashes, which can cause scarring or even infection. The list goes on; find your correct size!

Other Sizing Solutions and Troubles

If you are still finding that your true size or your sister sizes aren’t cutting it, and you need a little extra to help your bras out, there are some other solutions available. One common problem solver is the Rixie Clip. This clip is advertised as a bra band extender or tightener (depending on your needed application). Its design is simple, but a bit like trying to write you name with your left hand. The potential downside to this little device is that it can put your bra straps in a position which is either too narrow or too wide on your back. If they are too narrow, they wight dig and pull at your posture. Too wide, and your straps will be falling off your shoulders for the majority of the day.


If you’re unsure of your calculated size because it sounds super foreign to you, that’s okay! If you need a good place to double check your measurements, go here. This site, Sophisticated Pair, has a simple calculator that you put your 2 measurements into. It shows pictures of how your measurements should be taken. Also, it asks you how you like your bras to fit (more snug, loose, etc) and will give you a sister size recommendation accordingly. There are also tons of other useful links to check out.

No matter how difficult it is for you to find a bra that you adore, always remember to love yourself, too. It can be excruciatingly difficult to find clothes and bras that fit our big chests, but this isn’t any fault of our own. Simply because we didn’t develop our bodies to fit the agenda of some random lingerie designer doesn’t make us criminals. I’d be surprised if most bra designers knew much of anything about the human body, anatomy, physiology, or the female figure specifically! But don’t lose hope, there are tons of great designers and manufacturers out there to be discovered.

If you’re fond of a particular brand, please feel free to comment and rave about their wonderful products. If you have questions, concerns or funny stories, please also share. I love to hear your feedback!

If you enjoyed this article, then we're probably very similar. I'm Victoria Melo, and I know what it’s like to be busty and struggle finding the perfect bra. Not long ago, I was just another girl wearing the wrong bra size. When I finally discovered my real size and found great bras for my busty figure, it felt like a miracle. Now, I'm a bra fitter helping hundreds of women like you find their own miracle. Click here to read my lists of my favorite bras for you.
Nice to see you again. Would you like to get expert help to create your own Bustiest plan?YES, PLEASE!

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