A Cup vs B Cup Bra Sizes In Review

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An A cup and a B cup can sometimes have the same breast volume, but their bust and band size will be different. I discuss more differences between the A cup and B cup in my article below.

A Cup vs B Cup General Overview

The B cup is one cup size bigger than the A cup, which means the B cup is an inch bigger in the bust measurement when compared to the A cup.

A girl wearing a dark blue shirt holding a white laced bra

A Cup

An A cup is considered one of the smallest bra sizes available. It is three sizes smaller than a D cup, which is the average size in the US.

An A cup will look smaller on fuller-figured or curvy girls and will look bigger on smaller, more petite girls.

An A cup is usually the size that pre-teens and developing teenage girls wear, though this size is not limited to teens alone. Adult women can also be this size.

A A Cup bra size is when the breast size measures only 1 inch larger than the band size.

B Cup 

A B cup is also considered a smaller size, as it is only an inch larger than the A cup. However, plenty of petite and smaller chested women have B cup breasts.

A B Cup bra size is when your breast size measures 2 inches larger than your band size.

Similarities and Differences

A and B cups are both considered on the smaller end of the bra size scale. Both of these sizes are usually used by pre-teens, teenagers, though there are adult women who wear these sizes as well. It may be hard distinguish a B cup from an A cup because both of them can have the same cup volume

Comparing A Cup and B Cup Bra Sizes

Cup Size Bust and Band Difference Average Weight Best Bra Styles
A 1 inch1 poundWireless, bralette, bandeau
B 2 inches1.72 poundsT-shirt, demi, push-up
Comparing A cup bras to B cup bras with their key differences with a featured illustration of the upper section of two women wearing red bras in different cup sizes

How Big Are A and B Cups?

An A cup bra can be as small as 32A and as big as 38A. A cup breasts weigh on average one pound.

A B cup bra can be as small as 32B and as big as 40B. B cup breasts may weigh an average of 1.72 pounds.

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 size 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 to measure your breasts. The easiest way to do this is to take a tape measure and measure your bust and your torso. Here are steps on how to take your breasts’ measurements:

A close-up image of a blue colored bra

Measure Your Band Size

  • Remove your shirt and anything that may add to your band size. 
  • Wrap the tape measure around your torso, just below your breasts. The tape measure should be flat on your skin.
  • 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 get.
  • If it is an even number, add four. If it is odd, add five.

Measure Your Bust Size

  • Wrap the tape measure around your bust in the fullest part of your breasts.

Finding Your Cup Size

  • After taking the band and the bust measurement, subtract them to get your cup size.
  • If the difference between your bust measurement and your band measurement is an inch, then you are an A cup.
  • If the difference between your bust measurement and your band measurement is two inches, then you are a B cup.

Related Questions

Are A and B Cups Regular Bra Sizes?

Yes, A and B cups are among the standard bra sizes, which makes A cup and B cup bras easier to find, with many different styles to choose from.

What Does an A Cup Look Like?

An A cup looks small on a body, especially on muscular or broad chests, as it only has a one-inch difference between the bust measurement and band measurement.

What Does a B Cup Look Like?

B cups also look smaller on a body. This cup size will appear larger on smaller, petite women. They will appear smaller on women with larger torsos.

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

Which Cup Size Is Better?

There is no “better” cup size. A cups and a B cups are both considered small, but they are very versatile bra sizes, as there are so many styles of bras available for both A and B cups. Since A and B cups are smaller, they don’t need as much support and people who are and A or B cup can even go braless if they wanted.


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.