Bra Equivalents: Sister Sizes for 30b, 30c, & 30d

Here is all the information you need on bra sizes if you’re a woman. You want measurements that will properly support your bust, which is what this article will teach.

You’ll learn about the differences in cup sizes so you can find the lingerie that works across cup sizes. We’ll teach you the factors to look out for so you choose styles you’ll love.


The bra sister equivalent sizes of 30a are 28B and 32AA. The bra sister equivalent sizes of 30b are 28C and 32A. The bra sizes equivalent sizes of 30C are 28D and 32B. The bra sister equivalent sizes of 30D are 28DD and 32C.

Table of Contents

What are bra sister sizes?

Straps are digging into your skin, hanging loose on your shoulders, underwires leaving marks, or simply giving you no support whatsoever. If any of these cases are true for you, the size you regularly opt for just doesn’t fit you the same anymore.

Are you experiencing these issues?

  • The cup doesn’t hold everything in.
  • It’s bulging on the side.
  • The fit doesn’t seem quite right.
30b bra

Either it doesn’t fit you the same, or it never truly has. All bodies are unique, especially in bras. They must fit well around the torso, width of your shoulders, and bosoms. Given that there are so many brands and labels on the rack, one size couldn’t possibly be identical across them all.

Perhaps this is why you cannot find the correct fit in a particular brand, despite picking the right size. This is where bra sister sizes come in. You should go pick out a bra sister size instead. Bra sister sizes are practically similar to a particular bra, with only a few alterations.

For example, 34C, 32D, and 36B belong to the same sister family. They’re all identical in the cup but have variations in their band. In simpler words, they fit the same around the breasts. However, their fit around the torso is different.

Below are bra sister sizes for 30b, 30C, 30D, 30DD, and 30G in a convenient conversion chart so you find the right sister sizing:


If you’re a 30C but don’t feel like it:

Size up to 32B: Maybe you feel that the fitting of the cups in a 30C is great, but the band of the bra is way too tight. You should try a 32B. The back of 32B is 2 inches bigger, but the cup is the same.

30c bra

Go down to 28D: If you feel that 30C is way too roomy or baggy of a fit, we recommend you go for a 28D. The back of the 28D is 2 inches smaller, but the cup is the same.

30c pushup bra

If you’re a 30D but aren’t so sure:

Size up to 32C: The fitting of the band around your body is two inches bigger, but the cup is the same.

Go down to a 28DD: The back around this is two inches smaller, but the cup is the same. So it will be more snug around your back if that’s the issue you encountered with a 30D.

We also have these following guides on other clothing articles:

30d bra on a wooden floor

If you’re a 30DD at present, but your bras don’t feel right:

Go up to a 32D: The cup will remain the same, but 32D offers you a back two inches bigger. This is great if a 30DD was feeling tight around your frame.

Go down to 28DDD/28E: The cup will again remain the same. But because the back will be 2 inches smaller, it’ll offer you a cozier fit than a 30DD.

If a 30G isn’t doing you much justice:

  • Go up to a 32FF: The back of a 32FF is 2 inches larger than a 30G if a 30G was giving you too much compression to your body. The cup is the same.
  • Go down to a 28GG: If you’re looking for a tighter fit, the back of a 28GG is 2 inches smaller. However, the cup is the same.

What are the sizes of a bra?

The sizes of a bra are a combination of two things; a bra size and a band.

The smallest cup size available is an AA cup. At the same time, the largest cup size goes up to G, H, or HH and beyond. It depends on the brand you’re shopping for and its availability.

The smallest band (the measurement around your torso) starts from 28 and goes up to 50 and beyond.

Therefore when we put two and two together, bras vary from 28AA to anywhere betwee 50HH and beyond.

Where can you buy bras?

That depends upon you. We recommend shopping online at Amazon as the best place, given their free return policy. If something doesn’t fit right, you can always get your money back from the store for the undergarments you ordered.

Once you start shopping, you’ll find the most comfortable fits there. Once you find a brand you love, you’re likely to order from the same place again and again.

How to make them strapless?

There are two ways of wearing your bra strapless. That is without using any scissors! The easiest way is to remove the straps from a bra that fits you well. Take one strap and fasten it to one of the backsides. Then bring it around your body and attach it to the other back side.

The second way is to tuck in your strap inside your cups and wear a tight dress or top over it to keep it in place. This hack only works if your dress is well-fitted and can firmly retain the strap from popping back up.

How to hide straps

With so many options on the rack, it becomes difficult to find a bra that goes with everything. Don’t worry. Even if there’s everything from sleeveless, strapless racer backs to bulging necklines. Here are a few tried and tested tips you could try:

  • You could pick up an extra pair of invisible straps. These straps aren’t technically ‘invisible’ because you can still see them. Nonetheless, they won’t distract from that pretty formal dress you’ll wear to that big office party! Plus, they give you the support that a strapless bra wouldn’t be able to offer.
  • Does your top or dress have a racer back? Don’t worry; you don’t need to go out and buy a racer-back bra. You can turn your regular bra into a racer-back with the help of a paper clip. Just take the two straps at the back and bring them in. Entangle them into the paper clip. This way, they sit close together on your back.
  • If you have a really good-fitting one, you can attempt to turn it completely strapless. First, take out both the straps of your regular bra. Using just one strap, attach it to the back on one side. Then, take this strap around your body and secure it on the other back side. This will give you extra support under your breasts. Additionally, you could use some double-sided tape to attach the top of the cups (where the straps would usually be attached) to your skin.

How many should I own?

Five to six, or seven even, is more than enough for your wardrobe. Whether you’d like to stack 6 of the same kind or have each one serve a different purpose is totally up to you.

Whatever it may be, these bras should be a reflection of your lifestyle. We would like to give you the suggestion of keeping three everyday bras and three specialty ones. This is an arrangement keeping in mind that you’re somebody who lives the average life.

You do some work, party a little on the weekends, and work out. The three specialty ones could consist of a strapless bra, a sports bra, and perhaps the last one could be backless. If you sweat it out almost every day, you could make the last one a second sports bra.

You do you. Just take into account that if you were to do your laundry once every week or two weeks, your bras should last you just as long.

How should it fit?

With so many women wearing the wrong bra, it becomes essential to answer this question. When you wear it, the cups should contain the entirety of your breasts.

The breasts should not bulge out from the armpits. There also shouldn’t be any double breasts forming in between the cups. If any of the mentioned things are present, it means that the cup size is too small for you. Try one that is up a cup.

Alternatively, the cup could also be too big for you. You can check this by bending over and looking for any gaps between your breasts and the cups. If you can look inside the cups, then the cups are too big for you. Consider choosing a cup down.

  • The cup should hold the entirety of the breast.
  • There should be no bulge from the armpits.

Where to buy them

There is a bunch of places where you can go to buy them. Here are some of our favorite stores and places to start looking:

  • Amazon
  • Victoria’s Secret
  • Nordstrom
  • Asos
  • Bravissimo

You can easily calculate your size with simple math and a measuring tape. Just make sure that you’re wearing a comfortable bra (we don’t recommend a sports bra) before you follow the steps below:

How do I know my size?

  1. Figure out your band size.

    You will take your measuring tape and wrap it around your rib cage. Wrap it right underneath your breasts, where your bra or underwires typically sits on your body. Please take note of this measurement and add 3 inches to it.

    If your torso measures 29 inches, your band size would be 32. If your band turns out to be an odd number, then simply round it up a band. So if your torso measurement is 32 inches and you add 3, it would come out to be 35. We would round this number up to 36. Your band size would then be 36.

  2. Figuring out your cup size.

    Take the same measuring tape and wrap it around the fullest part of your breast. Wrap it snugly, neither too tight nor too loose. Subtract the band from this measurement.

    If the measurement around your breasts is a 40, and your band is a 36 (40-36), your result would be 4 inches.

    Now check your results in the chart given below:

  3. Put your cup size and band size together.

    Once you’ve figured out your band size and cup size, you can put them together for your ultimate size!
    Maybe you were a band size 36, and your cup size is 4 inches. You would be a 36D.
    While figuring out your size, here are some extra tips to keep in mind:
    If you encounter an uneven number, always round up to the nearest band size.
    If both your breasts are slightly different in size (which is totally normal), look for the correct fitting of your smaller breast.
    Suppose you go through the entire process above of finding your size but still don’t think it fits quite nicely. Go for its sister bra size. A sister bra size can easily be figured through this method as well:
    Go up a band size and down in cup size: Do this if you feel that the cup size is fine, but the band feels tight around your back and torso. So suppose you’re wearing a 32D. Going up a band and down a cup would mean you should try a 34C.
    Go up a cup and down in the band: Do this if you feel that the band feels too loose around your body. So if you’re a 32D, try a 30DD or 30E.

30d bra

Hopefully, you’ll be able to get the right 30b bra sister size that fits you right after having read this guide & article. Breast tissue is highly delicate and deserves the right attention.

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