A cup vs B cup what’s the difference between these cup sizes?

A cup and B cup women (or somewhere in between) often wonder about A cup vs B cup.

  • What is the difference between A cup and B cup?
  • Is B cup bigger than A cup?
  • How will I know if I’m an A cup or B cup?

Dobreva Floral Lace Everyday Lightly Padded Underwire Bra – AA-DD cups | See Dobreva collection at Amazon.com

What is the difference between A cup and B cup?

It’s a question I get a lot from my readers. What about A cup vs B cup bras? And I’m happy they’re asking. Why? Because if you’ll learn the answer to this question you really know all there is to know about bra sizing.

ThirdLove invented half-cups
AA to I cups Shop now
⭐ Herroom AA - M cups Shop by your size
⭐ Amazon Best Rated Bras Shop Now

It is very understandable for any woman not to wear a well-fitted bra. Bra sizes can be very close together. The same woman might actually fit more than one bra size. And all these bra sizes may fit her just fine!

So, it may seem cup B is bigger than cup A. But as it comes to bra sizing it’s just not that simple.

Is B cup bigger than A cup?

A cup vs B cup could mean
Instead of the 75A bra you’re wearing right now, you might need a 75AA, a 70B, a 80AA or a 80AAA bra.


Yes. It’s all about the fact that bra sizes might be this close together. A little change in measurements could mean you need a totally new bra size.

There’s also the possibility you might need a bra sister size. When just changing your band size but keeping the same cup volume it’s a bra sister size you’re looking for. For example, the bras 34B, 32C and 36A all have the same cup volume. Read more about bra sister sizing here »

a cup vs b cup
Measure a couple of times and write down the outcome

How will I know if I’m an A cup or B cup?

I’ve listed some points for you to score yourself. 

  • put on your bra and have a look in the mirror, how does it look?
  • does it really look good?
  • does it feel comfortable?
  • does its elastics fiber support your breast firmly, but still in a comfortable way?
  • do you feel your bra the whole day? Not in a nice way…
  • are you touching your bra a lot during the day (to keep it in place)?
  • will the bra make your clothes stand out?
  • do you feel confident wearing your bra?
  • do you feel womanly?

Just by answering these questions for yourself I’m sure you will know how well your bra is fitted. If you are not happy and do not call yourself a bra lover (just yet), it’s wise to do a bra size check.

It could be the elastic fibers of your bra are not strong anymore. So maybe your bra size is still correct, but your bra(s) need to be replaced. Read more about washing and taking care of your bras in the best way »

When I measure women and tell them they should be wearing another bra size they are never surprised!

Why? Because we see ourselves every day in the mirror and we feel our bra all day long. To change your bra size isn’t something you just do. Especially if you wore this size for long, maybe someone advised this size on you.

Lily of France Women’s Extreme Ego Boost Push Up Bra A-D cups | See collection Vanity Fair at Amazon.com

How to measure and find your true bra size in 10 minutes?

Instead of A cup vs B cup, I could have written any cup size here. No matter what size you’re wearing now, all women can find their true bra size in just 10 minutes.

measure tape bra difference a cup vs b cup
Knowing your sizes will make shopping more fun!
  • first, measure your underbust and write down the outcome
  • secondly, measure your bust size and write down the outcome

The last step is to check your size in size chart, finding the matching bra size.

If you have small breasts be sure to check a size chart that includes all small sizes! Or use the bra size calculator. And please play around with the measurements a bit. This will show you whether you might fit more than one bra size. Depending on the model and brand you’ll know the alternatives you have. In the end, you’ll know which size feels best on you.

Go to bra size calculator and determine your best bra size

Amazon AA cup bras »

Amazon A cup bras »

Amazon B cup bras »

Amazon C cup bras »

Video Top 10 for petite ladies by Herroom

How To Measure Your Bra Size
Bras For Women With Small Cup Sizes
Bras For Strapless And Backless Dresses
Best Bra Styles For Deflated And Pendulous Breasts
Best Bras For The Plus Size Petite Woman
Cleavage Defined: The Hidden Truth