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Tomima Talks: Decoding Bra Cup Sizing

When shopping for clothing, we know there are typically 5 sizes to choose from, such as XS, S, M, L, XL, or 2, 4, 6, 8, 10. This is not the case with bras. Guess how many sizes the average bra comes in?  Twenty-four.  I recently asked one of my webmasters to do a few queries for me and found that HerRoom carries bra styles that actually come in 99 unique sizes.  He also informed me that HerRoom offers for sale a total of 505 different bra sizes!  With this mountain of options, why are so many women in the wrong bra size? I’ve concluded after 20+ years in the industry that this is primarily due to the fact that once a band size change is needed, most women don’t know how to choose the correct bra cup size to compensate. If you are larger than a DD, this becomes even more challenging because multiple sizing conventions come into play. Let me also make clear that this is not your fault. The system is not intuitive. And, there’s no place to go to actually learn how to do this… until now.

Changing cup sizes when you keep the same band size is easy – you just move up or down a cup size. However, a bra size change in cup size only is pretty rare – most women who maintain their same band size don’t very often need to change their cup size. But, when weight gain or loss occurs and a bra’s band no longer fits the same, most women don’t understand what their next bra size should be.  After all, unlike other articles of clothing, a bra is a combination of two sizes – cup size & band size – and each of these sizes can independently change by getting smaller or larger.

There is a method to what seems like madness in the world of bra cup sizing. Once you know the system, bra shopping should be much less frustrating.  Here it is:

Cup Sizing Is Based on Breast Projection

Allow me to explain this using the cup size D as my example. All D cups (regardless of the band size they are attached to) have the same projected distance off the wall of a woman’s chest.  Take a 34D bra and a 38D bra. Both have the same distance or projection from a woman’s chest or ribcage. But they are different in their volume because the base of a 38D breast is larger.  To try and better explain this, below is an exaggerated illustration of my point from a bird’s eye view looking down at a woman’s chest.

The base (or root) of the breast that rests on your chest gets a larger circumference with each increase in band size.  This next illustration is a straight-on perspective of the same bra sizes as above but in a more realistic volume increase, which is small and subtle. This straight-on perspective shows that the breast circumference and breast volume increase with a larger band size even though the cup size letters stay the same.

I hope this explains why you don’t want to keep your same cup size letter if all you want to do is move up or down a band size. If you do, your cup volume will change and the bra will not fit. This is the most common error women make when adjusting their bra size. Here is one more image to reinforce this point. My team created this shot for me.  We pulled a series of D cup bras in the same style but different band sizes. We then lined them up in ascending band size order.

Note how the vertical lines splay out as the band size increases. The cups are getting a little larger with each band increase –  they are increasing by one full cup size, though all are D cups. And here’s an homage to bra manufacturers; each of these four D cup sized bras must also have their own unique underwire size to adjust to the expanding base of the breast.

Cup Sizing Rule 1:

Moving up 1 band size – 36D to 38D – also increases your cup volume.

Moving down 1 band size – 36D to 34D – also decreases your cup volume.

Cup Volume Changes with Band Size

When your bra band starts feeling tight on its loosest hook, it’s time to move up a band size.  I just explained above that moving up a band size also increases cup size volume. If your breasts have also increased in size, moving up a band and keeping your cup size the same gives you an increase in both – so that’s your new bra size and it fits.  Conversely, should you lose weight, and your breasts lose some fullness, moving down a band size and keeping the same cup size gives you a decrease in both – so that’s your new bra size and it fits.

Weight loss and weight gain often do not impact our breast volume – breast volume and size stay the same.  It’s these scenarios where most women make the incorrect choice in selecting their next bra size to try.  And, it’s completely understandable. Without knowing how bra cup sizing is determined, you would never think to try the size I’m about to recommend. It simply doesn’t make sense.

When all you want in your next bra size is a bigger band, your next bra size move should be to go up a band and down a cup size.  Conversely, if all you want is a smaller band, your next bra size move should be to go down a band and up a cup size.

The above illustration shows you the same cup size volume on three different band sizes. All three of these bra sizes (34DD, 36D & 38C) have the same breast volume and thus the same breast base diameter.  Also, note that the cup sizes are descending with each increase in band size.  Going down a cup size as you move up a band size compensates for the added volume increase a larger band size creates.  And, going up a cup size as you move to a smaller band size gives you the volume you would otherwise lose moving to a smaller band size. My team took the same bra in my earlier example above, and this time increased the band size while simultaneously decreasing the cup size.

See how the lines this time stay parallel as the cup size descends and the band size increases. This shows the cups are the same size in all four of these bra sizes.  In fact, all four of these sizes are made using the same size underwire.

Cup Sizing Rule 2:

Moving up 1 band size & down 1 cup size – 36D to 38C – will maintain your cup size volume.

Moving down 1 band size & up 1 cup size – 36D to 34DD – will maintain your cup size volume.

Some Final Thoughts…

I get that this may be a lot to take in.  It’s not intuitive, but there is a reason for it.  I also made a bra cup design and size video that might help you with this concept.

With retailers going out of business, along with lingerie specialty stores, I worry that all the great fit help they provide is slowly going away.  If this continues, women will need to understand the bra sizing system to make the correct size change adjustments.  I hope this little tutorial helps


Tomima Founder & CEO

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