How Big Is a 30B Bra Cup Size?

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Wearing a perfect-sized bra is a game-changer. It offers support in the right places and feels incredibly comfortable. If you are unsure about your measurements and wondering if a size 30B will fit you, you have landed on the right article.

Here I explain exactly how big is 30B. Keep reading!

How Big Is 30B?

In the size 30B, the band size that wraps around the underbust is 30 inches. The size “B” refers to a 2-inch difference in the band and cup size. Therefore, people with a 32-inch bust size and a 30-inches band size will fit comfortably into a 30B bra. 

Graphic image explaining that a 30B has a bust size of 31-32 inches and a band size of 29-30 inches with a featured image of a woman wearing a blue tank top and black shorts

The size of the bra is determined by two variables. These include the band size, which is denoted by the number, and the cup size, which is indicated by the alphabet. The alphabet identifies the cup size, which is determined by the difference between your band size and bust size. 

Are 30B Breasts Considered Small?

Generally speaking, a 30B is considered to be a smaller bust size.

If you have a band size of 30 inches, it means you are small and have a slim figure. A B-cup size would suit your frame as it is proportional to your body. The size is also near to the average bra size, with even smaller sizes. 

For petite women with smaller breasts, like a 30B, give my #1 recommended push up bra a try: the “Maidenform. This specific bra is super comfortable and features Wonderbra technology to give your breasts a nice lift!

If a 30B is snug around the bust, you might do better with a 30C bra cup size.

However, if you compare the size with the average bra size in the United States (34DD), 30B is relatively smaller than DD cup sizes. That being said, the average bra size varies in every country depending on the genetics of the nation.  “Maidenform Depending on your hereditary traits, 30B might be the perfect size for you.


Let me conclude by saying that every breast size is attractive. As long as you wear the right bra, it can accentuate your curves and highlight your breasts.

You can minimize or accentuate your breasts depending on your choice of bra, such as if you pick a push up bra or a bandeau bra for your innerwear. As a result, you can pull of any fitted dress or top fabulously. 

Woman holding a mug while wearing a green bra

Can I Wear Any Other Bra Size Other Than 30B?

Yes, you absolutely can wear a different bra size. Basically, different brands can have slight variations in their sizes. Consequently, while you find that 30B is the perfect fit for you in most brands, other 30B bras might feel awkward or even painful to wear

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

Moreover, it can also happen that you fell in love with a design but are unable to find your size in it. In that case, you can opt for one of the “sister sizes”. These refer to the sizes that go up a band size and go down a cup size and vice versa. 

In simpler terms, a 30B would be approximately equivalent in size to 32A and 28C.  A bra size of 32A has an underbust measurement of 32 inches and the bust measurement of 33 inches. Whereas, a 28C bra has a 28-inch underbust and a 31-inch bust.

30B Bra Size Details

30B SizeDetails
Band Size29 to 30 inches
Bust Size31 to 32 inches
WeightAround 1 pound
Sister Size Up32A
Sister Size Down28C

Related Questions

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

You’ll know if you have a 30B size if your underbust measures around 29 to 30 inches while the overbust ranges from 31 to 32 inches. You have B cups if there’s a two-inch difference between the band and cup sizes.

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

The best bra styles for 30B are those with seamless cups, thin fabric, and multiway straps. This small size easily lets you choose t-shirt and sports bras, as well as bralettes.

How Can I Make My 30B Size Look Bigger?

You can make your 30B size look bigger in many ways, including using padded bras, adding chicken cutlet inserts, or stuffing your bra. It also pays to improve your diet and exercise to put more fat in your chest.

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


A 30B size bra will seamlessly fit a woman with an underbust size of 30 sizes and bust size of 32 inches. However, if you are unable to find this size in a design you like, you can always go for a 32A or a 28C. As long as you have tried out the bra and it does not feel ill-fitted and uncomfortable, it should work perfectly well. 


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.