#AllChestsWelcome: The Cup Size Conundrum

While working on a recent muslin, I came upon a one of those funny little things about women’s patterns that makes no sense outside the Snowglobe of Sewing — the annoyance of “cup size.”

Of course, when I say “cup size,” I don’t mean bra cup size. Bra sizes (in the United States, at least) are chosen by measuring your under bust circumference (to find your band size), and then your full bust circumference. The difference between your full bust and your under bust will dictate your cup size, in theory.* In garment sewing, though, “cup size” refers to the difference between your high bust measurement and your full bust. So, in essence, you are measuring the amount of projection between your high bust and full bust, or the amount your chest extends outwards.

Gabby's dressform, with three lines overlaid, marking the underbust (the circumference underneath the breasts), the full bust (the circumference at the fullest point of the breasts), and the high bust (coming up under the arms and over the upper part of the chest, above the breasts).
Dressform annotated to show where to measure high, full, and under bust circumferences.

For example: a typical pattern is drafted for a “B cup,” which is a 2″ projection from high bust. 3″ = C, 4″ = D, etc. This then tells you what size to make, by matching your “cup size” to the pattern “cup size”. (For more information on sewing pattern cup sizes, see this excellent guide from the Curvy Sewing Collective.)

What’s so confusing about this? The alphabetical naming convention. We already measure bra cups in “Alpha” sizes — why call something else a cup size, using the same letters to differentiate it as bras already do, but have it mean something completely different? If you end up choosing a pattern size based on what bra cup size you wear, there’s a very good chance your garment won’t fit. Why call something a name that means something patently different everywhere else, except for this one tiny niche? It makes no sense to me! This is incredibly confusing to many sewists, new and seasoned alike.

I wanted to find out if there was some history behind this convention, so I popped on my deerstalker, and networked my way into a conversation with a friendly soul who works for the Big 4 pattern companies. It appears this method of choosing a size, or using a pre-drafted cup size pattern piece, is based on the idea that garments are fit on a model who is a specific cup size — for straight sizes this is usually a 36B, as it is also in most RTW apparel. There’s even an explanation on the new Something Delightful website (the home of the Big 4) about how to measure this — which, while helpful, isn’t explicitly clear on printed pattern envelopes.

My source mentioned that of course, the best way to get a good fit using this method is to tissue fit or muslin. I agree!

But what about if your high bust and full bust measurements are the same, or don’t have a typical difference? My source and I also agreed on this one — measure the shoulder on the pattern and your body, and also check your actual bra cup size, if applicable, or the difference between your full bust and underbust. If there’s a significant difference, choose based on your shoulder measurements and make your own full/small bust adjustment.

There are so many factors that come into play that can complicate a high bust measurement: the width of your shoulders and back, how high or low breast tissue or muscle sits on your ribcage, and even what undergarments you are wearing. Push up bras and binders can give you a larger high bust measurement by lifting some of the breast volume up there, and wearing something with less anti-gravity properties will yield the opposite.

To get to the heart of the issue, I’d like to suggest that we stop referring to the way things are drafted as “cup size,” and instead call it “chest projection.” This not only eliminates confusion, but it removes cultural bias inherent to the terminology, and it’s gender neutral, for all those non-binary folx in our people spectrum. The actual method in which pattern drafting or personal adjustments are done shouldn’t need to change, but instead of calling things B, C, and D cup sizes, they can be called 2″ chest projection, 3″ chest projection, 4″ chest projection, etc.

The reason I am proposing this is because chest projection itself encompasses many things — fat, muscle, breast tissue, ribcage angle, and so on. I think that referring to that measurement as a “cup size” is disingenuous; cup sizes themselves, referring to a bra cup, also take into account breast shape, drop, and breast placement on the ribcage, all things that are not specifically accounted for in a “cup size” pattern draft. The term “cup size” is very gendered, using specific terminology based on people with breasts.

Cup size drafting relies on circumference and vertical measurements, but only in certain categories (intimate apparel and swimwear for example) does it actually base itself on the way a fit model’s individual breasts are shaped on their individual skeleton. Calling chest projection “cup size” in garment sewing is needlessly confusing, unless there is actually a cup in the garment (hello, evening wear!).

A further point: drafting patterns according to chest projection is a good starting point, but depending on your apex placement (the fullest circumference point of your chest measured vertically from your high point shoulder), it may be less helpful to use a pre-drafted “cup size” piece. If you are shorter, or have a higher apex, for example, you will probably still have to raise the armholes on styles that have “cup size” extensions. I have a 5″ difference between my high bust and my full bust, but my apex placement is a standard ~11″, which is around what a B cup draft placement would be. However, apex placements are graded vertically from that base size, so a D cup pre-draft apex is way too low on my body.

Gabby's dressform, in a 3/4 view, showing how to measure from the high point shoulder (where the shoulder meets the neck) to the apex (fullest part of the bust). There are also arrows to show the chest projection where the bust is fullest.
Dressform annotated to show where to measure apex placement, and visualize chest projection on a torso.

In conclusion: let’s throw “cup size” wording out the window and adopt “chest projection”. It’s certainly easier to understand and explain. I know I’ll be making that mental change the next time I pick a pattern size!

* Of course, and slightly OT, there are bra companies that will have you measure your high bust when determining a band size. However, I would beware of that method. Depending on your breast shape, and where your breast/muscle begins on your chest, you may not get an accurate circumference measurement.

Gabby is a technical designer, fit specialist, and prolific googler. She lives in Denver, raises tiny littles, reads, embroiders, makes, experiments, fails, learns, tries again. See her on instagram @ladygrift.