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.

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.

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.
Thank you for this. I also heard Andrea of Sew To Fit mention this in one of hear videos . Great minds think alike.
My pleasure! Ohhh cool I’ll look it up- thanks!!
That was very clear and helpful, thank you!
Of course, thanks for reading 🙂
What a great article and I totally agree with you. I have a large bust, high waist and narrow back/shoulders. Chest projection works for all these but using cup size – bra or dressmaking – means loads of alterations. I can’t be the only one out there not an industry standard across torso!
Definitely not- there are so many people who have issues fitting torsos for all kinds of reasons, I feel like why make it more confusing than it has to be? Thanks for reading! 🙂
Lightbulb moment!! Thank you so much – I didn’t understand why my FBA calculations always showed I didn’t need one even though I’m a 32FF. I was convinced that I was measuring incorrectly.
There are always so many things to account for, aside from the obvious 3-4 circumference measurements, there’s no way everything will fit out of the envelope every time. Good luck sewing! 🙂
Honestly, this is so helpful to me! I’m not sure the answer for myself, but my measurements suggest a D sewing projection/ cup is what I need. I have tried the D and they still don’t fit right. I tend to get a good fit by choosing for my upper bust and making a FBA from there. The D cup still smooshes me.
I couldn’t agree more! I have so many issues with cup sizing in patterns – I wear a 34H or 32I bra size, and the bust darts are invariable too low on me. When I choose a pattern based on my high bust measurement, often the back is still too wide because I’m narrow across the ribs, but the chest projection is too small to fit my bust, so I get weird wavy side seams. My underbust measurement is a good 4 ½ inches smaller than my high bust measurement… So many things to take into account! I saw a video by @petitestitchery which explained how to measure chest projection, and measuring that way bumped my “sewing cup size” up from C to H, which makes far more sense for my build.
Also, I hope your suggestion will be adopted by pattern designers soon, if only for its more inclusive nature!
I’m a 32K and feel your pain! Sounds like we have similar issues- I like to take two sets of measurements, front and back bust (just kind of imagining where the side seam should hit), and that helps with the wavy side seams knowing that my front piece will always be bigger than the back, haha. I hope so too- thanks for reading! 🙂
I’m in the same boat!!!! 34M and broad shouldered but according to the traditional cup size measurement for patterns, I am only an “e” cup….. I really like this approach!
excellent, let me know if you try it! 🙂
I’m so excited about this series! I have a ~1″ chest projection and have to make an SBA for almost all patterns. Looking forward to learning more about making bust adjustments when modifying patterns!
Great, thanks so much for reading! 🙂
1/2 inch here. 🙄
[…] The Sewcialists post also explaining bust & cup sizing as relates to sewing. Love the positivity of this community! […]
Hi Gabby – This is so helpful. Thank you so much for the info about apex placement and ‘cup-sized’ patterns. My question is: if I have a high apex but a larger chest projection (usually a D), am I better off choosing the B pattern piece and doing an FBA, or the D piece and raising the apex and/or armhole? I’m planning on making a shirt.. Thank you!
Hi Janet! I’d say it depends on the pattern- if it’s like a tee or something super simple, use the D piece and raise it. If it’s like a button down woven or something more complicated, I’d recommend doing your own FBA on whichever size matches your across shoulder measurement, so you don’t have to mess with the sleeve and the armhole on something more fit critical. Thanks for reading! 🙂
Fab, thank you Gabby
You’re welcome! 🙂
Thanks for saving me…time and frustration. The new “cup sizing” is very misleading. My vote goes to “Chest Projection”.
P.S. I’m wondering if you’ve addressed forward shoulder adjustments?
I haven’t yet! Do you have a specific question, or just about shoulder adjustments in general? I can add to the queue for sure 🙂
I’m interested in the forward shoulder adjustment because my shoulders are definitely “forward”! However I don’t seem to have the shoulder slippage people talk about as their reason for making the adjustment. My problem (I think) is that the front of my garments tend to be too broad. (Extra room. ‘Gapage’ – is that a word?)
For example, after playing with the front of my toile of Vogue 9253, I was able to overlap the “deep V” of the bodice for a great fit… And that was after going down a size… And buying another pattern. (Ugh… But Ankara save!)
As I reread this I’m wondering if this is a cup size or forward shoulder issue?