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Yes, math! We love math! Yay math!!!

Dun dun duh... Dun dun dun dun duh...

So, bra sizing is confusing. We got that, we tried to clear some of that up. But as Hel pointed out, there seems to be a major discrepancy between What We Were All Taught about bra sizing and Bra Reality.

Basically, we were told that cup size is determined by the number of inches difference between our underbust and bust measurements– 1 inch = A cup, 2 inches = B cup, and so on. Based on this, many of us assumed this meant that all A cups were the same size/volume (i.e., “1 cubic inch” or some such), all B cups were the same size/volume, etc., and that the only difference between, say, a 32D and a 36D was in the band. But nay, as our own photographic evidence suggests, this is not true. Your 36D has significantly more volume in the cup than your 32D, in addition to being wider in the band itself.

A dramatic reenactment:

Pretend that this is a 32D.

We think a 36D looks like this (bigger band)

...but this is the real 36D (bigger cup, too).

Alright, then, so what explains the discrepancy between the 1-inch measuring system and the reality of “proportionate cup sizes” that vary based on band?

It turns out there isn’t a discrepancy.

How’s that? Well, your eighth grade math teacher told you that you’d need geometry in your “real life,” but you didn’t believe her, did you? Turns out, she was right.

The issue here is that your underbust and bust measurements are one-dimensional. They measure length (really, perimeter/circumference). Thankfully, our boobs are not one-dimensional. They’re three-dimensional, and as it turns out, a 1 inch difference in perimeters equals more than a 1 inch difference in cup volume, depending on the length of the perimeters.

Okay, okay, okay. Let’s try a visual aid. We’ll keep it at two dimensions* for simplicity’s sake. Hahahahaha, “simplicity.”  I crack myself up.

Alright. Let’s say we have two yummy, fictional, perfectly square, two-dimensional GIANT cupcakes.

Mmmm... Boobcakes...

Delicious Cupcake #1 is 8″ long on each unfrosted side. If it were a person, it would have an underbust measurement (perimeter) of 32″. With its frosting (aka boobs), it has a bust measurement (also a perimeter) of 36″, because it’s now 10″ long (8+2) on two of its sides. 36″-32″ = a 4″ difference, and in a land where 1″ = A, 2″ = B, 3″ = C and 4″ = D, that means Delicious Cupcake #1 is a 32D. Hubba hubba!

Fabulous Cupcake #2 is much the same, it’s just a little bigger overall (9″ on each side, for a 36″ “underbust”). 2″ layer of frosting on top, same 4″ difference in bust and underbust measurements = 36D overall.

Fine so far– we’ve proven that What We Were All Taught (the inch system of determining bra size) is pretty much on target. But what explains the difference in actual D-cup volume? Well, in this case, frosting area = boob area, right?

The frosting area of Delicious Cupcake #1 = 2 inches x 8 inches = 16 square inches.

The frosting area of Fabulous Cupcake #2 = 2 inches x 9 inches = 18 square inches.

Ta Da!

Ladies and gentlemen, there you have it. A 4″ difference in underbust and bust measurements always equals a D-cup**, but the bigger your underbust measurement, the bigger the volume of breast covered by a D-cup.

Yes, both things are true at the same time, thanks to the power of math!

I think you owe your geometry teacher a letter of apology.

*The third, which represents the “height” of the breast (from about the armpit to below the bust) is similar in all bras and just compounds the volume effect.

**Assuming this is the way a given bra manufacturer sizes its bras, and it usually is.

Related posts:

1. [...] Size Chart Woes: Fun With Math! « The Pretty Year // July 7, 2009 at 5:54 pm [...]

2. OK a post this butch can use! Now where do I get some of those cupcakes?

3. I don’t know whether to be amused or angry that the first possibly related post that comes up (MEASURING FOR YOUR CORRECT BRA SIZE) contains a horribly incorrect method.

4. Yeah, Sara, WTF? I have heard that “add five inches” advice before, and I just don’t get it. If I did that, I’d be wearing a 38 or 40 band (my measurement is under 34″), and even the PITA old lady bra fitter* at a venerated specialty shop had to agree that the 36s she brought me were WAY big, even on the tightest hooks. Like “boobs falling out the bottom of the cups” big.

Bra sizes do vary based on the manufacturer, but not as much as clothing sizes (IMO), probably because there are more of them, and they’re more specific. I *do* think that some are better for women with more or less fat/muscle on the ribcage (you could be skin and bones and measure 34, or be a very smushy 34). And of course, some manufacturers are better for a certain shape of breast, or perkiness, or spacing between the breasts, etc.

But this 5″ thing? I don’t see how that would work for any manufacturer. Even Wacoal, which runs small in the band… I wear a 34, and might be able to wear a 36 on the tightest band, but not a 38 or 40. No way.

*Old lady bra fitters are usually the best, but this one was obnoxious.

5. Hi Michelle. I’ve been reading your blog and I love this post and the “Size Chart Woes: The Naked Truth About Bra Sizes” articles. I would love to tell our readers at The Lingerie Post about them, because they are SO thorough and informative. I was thinking that I could post the first couple paragraphs on TLP and then link to your blog so people can read the whole posts?

Please email me and let me know what you think. I hope it’s OK I’m leaving a comment – I didn’t find an email address anywhere on the site. Thanks!

6. Thanks, Kelly, I’m happy to share! I will email you.

7. [...] Whew…  Fashion is tough!  Maybe I should stick to math. [...]

8. Nice insight!, the main issue here is that cup size is always a *constant* difference, which makes a same difference behave differently with different bands.

I always tell this to friends who ask me, to remember that the same cup size won’t look the same on different band sizes, since it doesn’t change proportionally, a B cup on a 28 band will look bigger than on a 40 band, because 2″ difference is more significant for 28″ than for 40″, although the 40B will be holding more “boob”

This also explains how is constant cup sizing is the problem with smaller band bras.
http://www.bratabase.com/blog/2009/jul/03/how-significant-is-an-inch-81/

9. Most definitely, JJ. At the same time a 40D is bigger, a 28D has a greater boobs-to-girl ratio in the minds of many. All this math and crazy charting just goes to show– folks need to wear what fits, and try not to get hung up on what the numbers and letters “mean,” YK?

10. Okay, I definitely want a cupcake after reading this!

Good analogy. I wish more women (myself included, several years ago) knew this information. I was SO convinced that based on the dress size I wore I could never wear a smaller band size, but once I dropped down 2-4″ in band size and went 2-4 cup sizes up (depending on the brand and the style) I got SUCH a better fit and my bras lasted a LOT longer, too.

11. Mmmm… Cupcakes. I’m not a small girl myself, but anything over a 34 band practically falls right off (or rather, my boobs fall right out the bottom).

12. [...] talks about math and boobs. For those of you looking for a great store to get sized correctly, check out Intimacy. I went to [...]