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

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An A cup and a B cup bra have a different cup volume if they are of the same band size. A’s and B’s can actually have the same volume if you vary in band size.

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What is the difference between A cup and B cup?

It’s a question I get a lot from my readers. What’s the real difference between an A cup and a B cup?

And I’m happy they’re asking. Why? Because if you know the answer to this question you really know all there is to know about bra sizing.

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?

woman holding measuring tape in article about A cup vs B cup
A slight change in measurements can change your bra size outcome

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 wanting to keep 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 »

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

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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?
  • have your breasts changed after a period of breastfeeding your child?
  • have you gained or lost weight?

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.

Sure about your A cup? Have a look at our A cup guide with all the best brands for A cup sized ladies »

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 on how to handwash your bras so you can enjoy your precious lingerie longer.

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When I measure women and tell some of 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 when needed isn’t something we act upon easily (happened to me). Especially if you wore this size for long and maybe someone advised this size on you.

  • If you have small breasts be sure to check a size chart that includes all small sizes!
  • Or use our 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

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