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Which is bigger cup size B or C?

When it comes to bra sizes, many women wonder which cup size is actually bigger – B or C? This article will provide a detailed comparison between cup sizes B and C, looking at factors like volume, fit, sister sizes, and more. Read on to find out which cup size is definitively larger.

What do cup sizes mean?

First, it’s important to understand what bra cup sizes actually mean. The cup size refers to the volume of breast tissue, not the actual dimensions of the breast. Cup sizes are proportional to the band size – a 30C will have the same cup volume as a 36C, even though the dimensions will be different. The cups scale up by 1 inch of difference between the bust measurement and band size. Here’s a quick rundown of how bra sizing works:

  • The band size refers to the circumference of the ribcage right under the breasts. This is represented by a number (30, 32, 34, etc).
  • The cup size refers to the volume of breast tissue. It is represented by a letter.
  • To determine cup size:
    • Take the bust measurement
    • Subtract the band measurement
    • Each 1 inch of difference represents going up a cup size

So if your underbust is 30 inches and your bust is 33 inches, that’s a 3 inch difference, making your size 30C. Now let’s look specifically at sizes B and C.

What is a B cup size?

A B cup means there is a 2 inch difference between the band size and bust measurement. For example:

  • 30B would have a 30 inch underbust and 32 inch bust
  • 32B would have a 32 inch underbust and 34 inch bust

Some key facts about a B cup size:

  • It is designed to fit breasts with less volume and projection compared to larger cup sizes.
  • The cups will be shallow rather than deep.
  • There will be less coverage of the upper breast area.
  • A B cup is one size larger than an A cup, and one size smaller than a C cup.

What is a C cup size?

A C cup indicates a 3 inch difference between the band size and bust measurement. For example:

  • 30C would have a 30 inch underbust and 33 inch bust
  • 34C would have a 34 inch underbust and 37 inch bust

Some key facts about a C cup size:

  • It is designed for breasts with slightly more volume and projection than a B cup.
  • The cups offer more coverage and are deeper rather than shallow.
  • It accommodates more upper breast fullness compared to smaller sizes.
  • A C cup is one size larger than a B cup, and one size smaller than a D cup.

Cup Volume Differences

Now that we understand how B and C cups are defined, we can look specifically at the volume differences between the two sizes. This will clearly demonstrate which cup size has more space.

Here is an approximate comparison of volume per cup for a 30 band size bra:

Cup Size Volume per Cup (cc)
B 140-170
C 170-200

As you can see, the C cup has a larger volume range per cup compared to the B cup. While there is some overlap in volumes, on average the C cup size is bigger.

For example, a 30B bra has a volume of around 140-170 cc per cup. A 30C bra has a volume of around 170-200 cc per cup. So the C cup size can hold more volume, meaning it is a larger cup size overall.

This pattern holds true across all band sizes – the C cup letter will indicate more volume than the B cup in any band size bra.

Shape and Fit Differences

Cup sizes B and C not only differ in volume, but also in shape and fit. Here are some key differences:

  • Projection:

    C cups are more projected and pronounced in shape than B cups. They protrude out further from the body rather than laying flat against the chest.

  • Coverage:

    C cup bras provide more coverage, especially in the upper cup area. B cups may leave the tops of breasts slightly exposed.

  • Balance:

    C cups have more room in the bottom of the cup, resulting in a more balanced, even shape. B cups may not completely encapsulate lower breast fullness.

  • Gap potential:

    B cups run a greater risk of gaping or the cup not completely filling out, especially for those with fuller breasts.

Overall, the C cup accommodates more volume and fullness while providing complete coverage. The B cup may cause fit issues like gaping, overflow, or lack of cleavage for those who need more projection and room in the cup.

Sister Sizes

Sister sizes have the same cup volume but different band sizes. Understanding sister sizes can help further illustrate that C cups have more volume than B cups.

Here are some examples of sister size pairs for B and C cups:

B Cup Sister Size C Cup Sister Size
28B 30B 28C 30C
32B 34B 32C 34C
36B 38B 36C 38C

Notice that the C cup sister size pairs have a larger band size than the B cup pairs. This indicates that C cups take up more volume in the same band size compared to B cups. The sister sizes scale up uniformly between B and C cups while maintaining the same cup volume. Again, confirming that C cups are bigger!

Common Misconceptions

There are some common misconceptions when it comes to B and C cup sizes:

  • Cups don’t equate to large breasts:

    The cup letter alone does not indicate how large or small the breasts are. Cup size is proportional to band size. A 30C is made for a smaller frame and bust than a 38C.

  • All D+ cups are huge:

    This is false – cups scale up incrementally in volume. There is not a major jump going from C to D. Larger band sizes like 36D or 38D may only have slightly more volume than a B or C cup.

  • A C cup is average or small:

    This depends on the band size. A 30C may be smaller in dimensions than a 36B. On average, C cups (and even D cups) are more common than most people realize.

The actual dimensions and aesthetics of B and C cups can vary significantly depending on band size and breast shape. Cup letters are just an approximation of volume – not an indicator of absolute size.


In summary, when comparing cup sizes B and C, the C cup definitively has more volume and room in the cup. It allows for more breast projection and fullness than a B cup bra. The difference in sister sizes also demonstrates that C cups take up more space than B cups.

While dimensions can vary based on band size and breast shape, the C cup on average will be larger than the B cup. So if you are deciding between B and C cups, know that the C will provide more coverage and accommodation for volume. Hopefully this breakdown has helped explain exactly how cup sizes work and which is bigger between sizes B and C!