How Big Is 30D Bra Cup Size?

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So many are wearing the wrong bra size their entire lives. This is mainly because finding the perfect bra is not as straightforward as picking the right dress size. Read on to understand how bra sizes work and find out the answer to the question: how big is 30D?

How Big Is 30D?

The bra size 30D entails that the bra band that wraps around your torso is 30 inches. In addition, the D cup size means that the bust size is 34 inches. It is important to note that not all D cup sizes have a 34-inch bust size.

If your bra size is 30D, your bust size has a measurement of 34 inches, with an underbust size of 30 inches

You can find your cup size by subtracting the band size from the bust size.

People who fit into D cups have a four-inch difference between the band size and bust size. This means that their boobs extend outwards four inches from their ribcage.

30D Bra Size Details

30D SizeDetails
Band Size29 to 30 inches
Bust Size33 to 34 inches
WeightAround 2.26 pounds
Sister Size Up32C
Sister Size Down28DD or 28E

How to Find Your Cup Size

To find out your cup size, you need to know your band size and bust size. To determine the band size, measure your torso directly under your bust. For the bust size, measure around the fullest part of your chest. Finally, subtracting the two numbers will give you your cup size.

If you feel like a 30D just isn’t the right fit, consider these options:

  • Instead, if there is a little too much room for your boobs, you might find that you fit a 30C better.
  • If a 30D is a bit loose around your torso, you should try a 30C or 30B cup size and tighten up the band.
  • Alternatively, if tight around your torso, you might prefer a 32D cup size.
  • If you find you’re spilling out of the cups, consider a DD cup size. Moving up in cup size, there is 30DD and 30DDD.

Most experts recommend wearing a non-padded comfortable bra so your boobs are held in the perfect place. This makes measuring your bra size a lot easier and your measurements more accurate.

However, if you are still unsure you can ask the experts at a lingerie store to help you find out your correct bra size.

Is 30D a Large Bra Size?

The D cup size often leads to the misconception of large breasts, but that is not always the case.

I have to remember that the cup size is relevant to the band size. Therefore, the breasts that fit into a 30D bra size are usually not very big.

However, how big your boobs appear depends on the overall shape of your body. 

Woman wearing a black bra

For example, size 30D breasts may seem voluptuous on a woman with a flat stomach and a slim figure.

On the other hand, the same size can look small on a woman with broader hips or wider mid-waist. 

Wearing different types of bra can also affect how your breasts can appear, as a padded bra can add volume, while a good bra can lift and shape them similar to push up bras.

For petite women with large breasts, like a 30D, you need everyday support. My favorite? The Elomi Banded Underwire Stretch Lace Bra. It has really supportive bands and a nice, three section cup.

Does Size 30D Exist?

Yes, the size 30D does exist. However, it is not very prevalent, making it difficult to find a bra in this size.

Nonetheless, you can always opt for one of the sister sizes, which have similar cup volumes. The sister size of any bra refers to the size that goes up a band size and comes down a cup size, and vice versa.

Graphic image with drawings of three white body mannequins representing the sister sizes for a 30D cup size

For example, a 30D bra size will be equivalent to 28DD, 32C, 34B, and 36A. While these sizes are good alternatives to your size, how well a bra fits you depends on your bone structure and overall silhouette.

Therefore, keep these sizes as backups when you absolutely love a bra design but cannot find your 30D size in it!   

Related Questions

How Will I Know if I Have a 30D Bra Size?

You’ll know you have a 30D bra size if your bust measures 33 to 34 inches while the underbust ranges from 29 to 30 inches. You should wear D cups when the difference between your band and bust sizes is four inches.

What Are the Best Bra Styles for a 30D Size?

The best bra styles for a 30D include full-coverage bras, sports bras, and racerback bras. It’s vital to prioritize lift and support when you have a 30D bra size.

How Can I Make My 30D Size Look Smaller?

You can make your 30D bust appear smaller using a minimizer bra, binder bra, or boob tape. You may also try darker and looser-fitting clothing.

Bra Size Measurement & Cup Size | A, B, C, D, DD Bra Sizes AND Extra Large Breasts


Women with a band size of 30 inches and a bust size of 34 inches can comfortably wear a 30D bra size. Despite sporting a D cup, these bras actually fit smaller breast sizes.

Since it is one of the most uncommon sizes, it is most often not readily available. However, you can always buy the sister sizes, including 28DD, 32C, 34B, and 36A.


Allena is the Founder and Editor of The Better Fit, a platform dedicated to empowering women with practical advice on bras and fitness, inspired by her own revelation of the widespread issue of incorrect bra sizing. Her expertise and tips have been recognized by major publications such as Cosmopolitan, Better Homes & Gardens, Insider, and NBC, making her a trusted voice in women's wellness and lifestyle.