Why Do Cup Volumes Get Bigger As the Band Gets Bigger?

One of our most popular blog posts is ‘Not All D Cups Are The Same’ which explains that the volume of D cups (all cups in fact) gets bigger as the band size gets bigger. This is why a woman wearing a 32E can also wear a 34D because the cup volume is the same, only the band is different.

This chart from the 'Not All D Cups Are The Same' blog shows Sister Sizing - bra sizes with the same cup volume

Lots of women were interested in the topic but asked for some more explanation. Today's post goes into more depth about why the volume of the same cup letter gets bigger as the band gets bigger. 

What Would We Look Like If All Cup Sizes Really Were The Same Volume?
As regular readers will know, cup sizes simply acknowledge the difference between a woman’s ribcage measurement and her full bust measurement. So for example both these women have D cup breasts because they both have a four inch difference between their ribcage and full bust measurements:

Woman A is a 30D (Ribcage = 30 inches, Full Bust = 34 inches)
Woman B is a 38D (Ribcage = 38 inches, Full Bust = 42 inches)

So why does Woman B with a 38D bust look bustier than Woman A who has a 30D bust? The answer is that Woman B's bust is PROPORTIONALLY bigger than Woman A.

To put this into context let's take the 30D breasts from Woman A and put them on women with 32, 34, 36 and 38 bodies to see what it looks like.
You can see that if all the women had exactly the same volume and size of breasts as Woman A then by the time you get to Woman B with a 38 body the breasts look pretty small (and quite far apart). In reality as our bodies get wider, so too do our breasts. The extra width doesn't just happen to our backs and band size, extra width applies to our breasts too.

Breasts Get Wider as Our Band Sizes Gets Wider
Here is the same diagram of 30 to 38 size women but this time the breasts increase in size in the same proportion as the body increase. You can see that the breasts get wider as the body does.

All these women are D cups because the difference between their ribcages and full bust measurements is four inches. To see why the breasts get bigger as the body does but the cup letter doesn't change let's take an aerial view of the breasts.

What Difference Does A Wider Breast Make to Cup Volume?
This diagram shows 30, 32, 34, 36 and 38 band women who all have the same depth breasts (this depth of breasts is always a D cup):
You can see that as the breasts get wider (but not deeper) the number of dots (i.e. volume) inside the breasts increases. The 30D breasts have 14 dots in them, then as the band size increases each breast increases by one dot. By the time you get to the 38D breasts they have 8 more dots inside them than the 30D breasts.

This is why the breasts on a 38D woman look much bigger than the breasts on a 30D woman, basically because they are. They are ALL D cups because they're all the same depth but their cup volumes are different because as the band size increases so too does the breast volume.

I hope that these posts and explanations of breasts helps you understand yours and other women's breasts better so please let me know if you find the explanations helpful or just plain confusing! The important thing to remember is that cup sizes don't say anything about the size of your breasts without the band size. xx