A Cup vs B Cup Bra Sizes In Review

As an Amazon Associate we earn from qualifying purchases.

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.


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.