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A Cup vs B Cup Bra Sizes In Review

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Would you believe that an A cup and a B cup can sometimes have the same cup size or volume? However, A cup and B cup can only be the same when it comes to the volume of the cup. Their bust and band size can be different. Let’s find out more about the A cup vs the B cup.

A Cup vs B Cup General Overview

Woman with an A cup wearing a red bralette

B cup is generally known to be one size bigger than the A cup. That is, the B cup is an inch bigger compared to the A cup. Aside from that, there are other features that you need to know about and A cup vs B cup. So here’s a general overview.

A Cup

An A cup is considered a small size among other cup sizes on the chart. It is three sizes down to D which is considered as an average size in the US. An A cup size may look smaller on full-figure or curvier girls and will look a little bigger on smaller and petite girls.

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An A cup is usually the size that pre-teens and developing teenage girls wear. Some teenagers may go up from AA cup to C cup. However, this size is not limited to teens alone. Adult women can also have this size.

B Cup 

A B cup is also considered a small size because it is only an inch larger than the A cup. B Cup is an average size when it comes to teens. Nevertheless, it is on the small section when it comes to adult sizes since it is considered smaller than average. 

A cup and B cup are related at some point because of their relative sizes. For example, if your size is a 36A, you can also wear a 34B. Moreover, if you are a 34B, you can also wear a 32C cup. It may vary from one person to another because not all breasts are equal. 

Similarities and Differences

A and B cups are both classified under the lower end of bra sizes. Similarly, these sizes are usually used by pre-teens, teenagers, and some adults. Sometimes, you may find it hard to distinguish a B from an A because both of them can have the same cup volume

Woman wearing a green bra

Though they may have the same volume, most A and B cups have different band lengths. The size of the band is very important when it comes to getting your proper measurement for a well-fitting bra. A slight measurement difference can affect the whole fitting and feeling of the bra.

How Big Are A and B Cups?

An A cup is commonly as small as 32A and as big as 38A which can have a measure of 27 to 38 inches. An A cup can weigh an average of 263.3 grams. Nevertheless, some sizing charts include sizes up to 64A and more.

Moreover, a B cup is usually as small as 32B and as big as 40B which is 27 to 39 inches in measure. A B cup may weigh an average of 447.5 grams. Similar to the A cup size, some sizing charts may include up to 64B which can always have an equivalent or sister size to C and D. 

Sister sizes for A and B cups are very helpful when looking for a bra. If your size is not available, you can go to a sister equivalent instead of going up or down a cup.

How to Know if You Are an A or a B Cup

There are several ways on how to take the measurements of your breasts. The most famous and easiest way to do this is to take a tape measure and measure your bust and your band. Here are steps on how to take your breasts’ measurements:

Measure Your Band Size

  • Remove your shirt and anything that may add up to your band size. 
  • Wrap the tape measure around your torso, just below your breasts. The tape measure should be parallel to the ground.
  • Try putting one of your fingers between your skin and the tape measure. Make sure that there is enough space or you might end up getting a very tight band.
  • Write down the number that you got.
  • If it is an even number, you need to add four and if it is odd, you need to add five.Woman with a B cup wearing a red bra

Measure Your Bust Size

  • To measure your bust, wrap the tape measure around your body along with the height of your nipple.
  • Keep it parallel to the ground. 
  • If your nipples are not projected or it is facing down, bending forward will help you get better measurement accuracy.

Finding Your Cup Size

  • After taking the band and the bust measurement, you just have to subtract them to get the equivalent cup size.
  • If the difference between the bust and the band measurement is an inch, then you are an A cup. For example, your bust size is 33 inches and the band is 32 inches. Their difference is 1 inch, therefore, you got an A. To be specific, 32A because of the band size.
  • If the difference between the bust and the band measurement is two inches, then you are a B cup. For instance, you got 38 inches for the bust and 36 inches for the band. Since the difference between these numbers is two, therefore your size is 36B. 

Which Cup Size Is Better?

It may be hard for you to identify which cup size is better. Since breasts are different in many ways, you cannot just single out one size and call it better. For you to get the perfect bra for you, make sure that you get the proper measurement. No matter the size of your bra is, it may look beautiful with the correct measurement.

A cup and a B cup are both considered small. Nevertheless, they can still give your body an accent once you get the right bra size. Remember that you do not have to go one cup up or down if A cup or B cup is not available. Just look for its sister.


Hi there, I’m Allena, Founder and Editor of The Better Fit. I’ve always had a passion for finding ways to help women improve various areas of their lives. I have researched and worked to create this website so women would have a place to come and be informed about an article of clothing they literally wear every day.