A few years ago, largely in the Capsule Wardrobe Sew Along FB group, we started talking a lot about sewing cup size. It’s a very useful concept, but one that can be very confusing if it’s new to you. So keep reading, and I will explain what it means and how I used it to know that I needed a small bust adjustment on my new Isla Top that I made as part of my Seasonal Sew 3!
Sewing Cup Size and What it Means.
What is sewing cup size?
Your “sewing cup size” refers to the difference (in inches) between your upper bust measurement, and your full bust measurement. It’s as simple as that. The sizing convention mimics bra cup sizing in that a 1″ difference between the measurements is an A cup, 2″ is a B cup, and so on.
For example, my upper bust measurement is 35″. My full bust measurement is 36″. So 36″ – 35″ = 1″. I am an A sewing cup.
However, and this is important, YOUR SEWING CUP SIZE IS NOT NECESSARILY YOUR BRA CUP SIZE. I will say it again: your SEWING CUP size is not necessarily the same as your BRA CUP size. They are two different things and must be measured separately.
Why would the cup sizes be different?
It’s fairly common for a sewist to have different cup sizes for their sewing cup and bra cup. I do. My sewing cup size is an A cup (36″ – 35″ = 1″ = A cup). My bra cup size, however, is a D cup. That’s because you calculate your bra cup size by taking the difference between your full bust measurement and your under bust measurement (or band size). My full bust is 36″, my underbust is 32″. So 36″ – 32″ = 4″ = D cup.
That’s all due to the fact that these measurements are meant to assess different things. The main purpose of sewing cup size is to approximate the size of your shoulders in relationship to your bust. Yep, you got that right. Sewing cup size is really about SHOULDERS, not about breasts. Bra cup size, on the other hand, it all about the size of the girls in relation to the bra band.
Where do you find sewing cup size in a pattern?
The short answer is you won’t. In fact, “sewing cup” is kind of a misnomer, because there really isn’t any “cup” involved. As I explained earlier, it’s just the difference between your full and high bust measurements. Increasingly, pattern designers are including the high bust measurement in their body measurement chart, and instructing customers to choose their size based off high bust in more fitted garments.
But if your pattern doesn’t list the high bust measurement, just know that B CUP IS INDUSTRY STANDARD. Frequently, though, patterns are drafted for a C cup. You can find a handy-dandy cheat sheet of some popular pattern companies here. This list is a few years old now, so it’s certainly not up to date, but has quite a few more well-known designers.
And if your pattern doesn’t include high bust, you can assume it’s drafted for an industry-standard B cup (unless you have information that says otherwise) and calculate it yourself. To do that, you will take the full bust measurement of the pattern, and subtract 2″ to determine the upper bust measurement.
As an example, let’s say we have a pattern that does not list upper bust measurements in the body measurement chart, and on that pattern size M indicates a 36″ full bust. To find the upper bust measurement (so you can assess size), you will take that 36″ and subtract 2″ for the B cup. That means that the size M in that pattern is likely drafted to a 34″ upper bust measurement.
Now you can take that upper bust measurement and compare it to yours to figure out what size you should start with. Make sense?
How to Use Sewing Cup Size
Ok, so now that you know how to find your sewing cup size, and how to find the pattern’s sewing cup size — what on earth do you do with it?!?
Well, sewing cup size is just another piece of information that can give you some clues as to how the pattern might fit you. It’s not a magic bullet, and it doesn’t always have all the answers. But it’s a useful place to start when assessing bust adjustments.
I’ll take myself as an example. The body measurement chart for this Isla Top includes the high bust measurement as well as the full bust measurement. As you can see from the chart, it’s drafted for a C cup (3″ difference between high and full bust). I am an A cup, which means that I probably need a bust adjustment.
My high bust measurement (35″) puts me in a M. My full bust measurement (36″) puts me in a S. The rest of my body measurements also say S:
At this point, you may think, well, 3 out of 4 of my measurements say S, so I guess I’ll make a S. But that is likely a mistake. Even though 3 of my 4 measurements fall squarely into S territory, the pattern instructs me to choose a M. That’s because I need a M to properly fit my shoulders.
I have broader shoulders. It’s much harder to adjust the shoulders of a pattern than it is to adjust the bust. That’s why I need to ignore that 3 of my measurements are saying S, and cut the M instead. From there, I’ll do a small bust adjustment to remove the excess width from the bust. That small bust adjustment will also remove width all the way down the garment. That ensures that it also fits my waist and hips. Pretty nifty huh?
My Isla Top
So that’s exactly what I did! I cut a M for this top, and then did a small bust adjustment to remove 1″ of width from the bust. (Tutorial for that is in the works!).
Now the reality is I probably could have gotten away without the bust adjustment simply because this top is drafted with quite a bit of negative ease. Even without the SBA, there would still be 3″ of negative ease at the bust. That’s why I only removed 1″ of width (for 4″ of negative ease) rather than 2″ of width.
On a top like this, that’s really a matter of personal preference. I decided to get a little closer to the intended fit with the SBA, and I’m really glad I did! The fit with the SBA is really great. The shoulders and upper bust are still wide enough for my body, but I don’t have extra bulk in the bust.
The SBA also removed 1″ of width from the waist. That brought the waist measurement closer to my own waist measurement as well.
So if you’re like me — broader in the shoulders and upper chest — using your sewing cup size to know that you need an SBA can save you a lot of time and ill-fitting clothes!