There's a lot of talk in the industry about the upper chest measurement, and I'm introducing sizing based on this measurement in my upcoming release, Herbalist. Here's what you, as a knitter, need to know.
What's the upper chest measurement, anyway?
The upper chest measurement is taken across the chest over the breasts, at a near-diagonal angle under the arms, and flat across the back.
Why does this measurement matter?
Everything I need to tell you about your upper chest measurement flows from one fact - sweaters need to fit your frame, and bust size is only weakly correlated with your frame size.
Put another way, sweater fit depends on your armhole depth, shoulder-to-shoulder width, neck width, ribcage circumference, and full bust - and full bust is the least critical and easiest to adjust. It's also a poor indicator of what the other, more critical, measurements will be. The other numbers all travel in a pack without a lot of variation - if you tell me your upper bust, I can probably guess pretty close to your shoulder width. But if you tell me your bust circumference, I would have a very difficult time. So why are we all picking our sweaters based on our full bust? That's like choosing a bra based on cup size alone!
Note - if you've been knitting sweaters for yourself using the ease at the full bust and you're happy with your fit, you don't have to change a thing!
How do I use this info?
Designers are increasingly providing sizing recommendations based on your body's upper chest circumference. In Herbalist, I recommend that knitters start by choosing the size closes to their actual upper chest body measurements. Then, take a look at how your full bust compares to the body circumference of the sweater. If the sweater is larger than your body (positive ease) by a few inches, this sweater will be comfortable as is. If there is little ease, no ease, or negative ease, you may want to work a full bust adjustment.
Note - if you've been knitting sweaters for yourself using the ease at the full bust and you're happy with your fit, you don't have to change a thing! Keep comparing your full chest plus ease to the finished measurement and choose your size accordingly.
Note - My upper bust is 38", making me a size D. Yet, I've been wearing my size B sample almost nonstop, and although I show it on Haley with 4.25" of positive ease at the full chest, it's almost 5" of negative ease on me, and I love it this way too! So trust your judgment with sizing, and when in doubt, measure an existing sweater that you love and compare it to the schematic.
What's a full bust adjustment (FBA)?
Many independent designers, myself included, use Ysolda's size chart - if you're curious, you can check it out here. If you crunch some numbers, you'll see that for busts up to around bust size 34", the chart expects an A cup, that busts 36" - 50" are a B cup, and that the rest of the sizes are a C cup. If that's you - great - you probably don't need this info!
For the rest of us, it's not uncommon to find that we're creating garments that either fit in the shoulder girdle but gap or pull in the front, or that fit around the bust but are oversized and slide around the shoulders and neck. To adjust, many knitters need to add fabric to the front. Depending on your preference and the design, there are a few different strategies for adding fabric to get around the girls.
Use short rows to add length
If you drop a piece of string from the tip of your collarbone to your hip, right past your underarm, that string will make a straight line. But if you run the string from your collarbone to your hip over your chest, that string will have some curves and be longer. One tactic to adjust the bust is to use short rows. By working back and forth across the middle of the front, you add rows to the middle of the front, but not the sides. If you're a sewist, this is the equivalent of adding a horizontal dart.
Or, add width
Alternately, you can add width - if the problem is inadequate circumference, after all, it makes sense to add to the circumference! There are two ways to do this - make the entire front wider to from the hem to the bustline, or work increases from the waist to the bust (If you're a sewist, these are like vertical darts!)
Like so much in knitting, which is 'right' is a spicy topic, but making any adjustment is better than wearing a poorly fitted sweater and you should try whichever one seems more intuitive for you! See the Go Further for more resources on this.
An all-over cable pattern makes a FBA tricky
The trick with working a FBA in knit sweaters is that often, there's a pattern we don't want to mess with! That's true with Herbalist - because it's an all-over cable pattern, it would be very tricky to work short rows or vertical darts. That means your best solution is to make the whole front wider, and since it's a raglan, this works very well because it suits the casual fit. To give you a head start on this, I've included in the Appendix some recipe-like instructions on how to add one or two inches of width to the front only (think of these instructions like a running start!).
Example: Your upper chest measurement is 38" - you're a size E. When you measure your full chest you find it's 41". The finished chest measurement for size E is 42.25". Without an adjustment, you'll have a trim 1.25" of positive ease. If you like that for your sweaters, this is the right size for you. I wrote this pattern with 3-5" of ease in mind, and it's shown in the pattern photos with 4.25" of positive ease. For your sweater to look more like the modeled sweater, you would want to add 2" in the front only, and possibly even go up to a size F with 1" in the front only.
Current trends in sweater fit
Right now, there's a bit of a trend towards deliberately 'ill-fitting' sweaters. I put that in quotes, because if it fits the way you want it to, obviously it's not wrong. But the style this year seems to be very little ease in the bust so that the front of the hem sits a little higher than the back without adding fabric - tilting the garment back. I quite like this style - I find it boxy, dramatic, and easy to wear, and that's the model on which Herbalist is based. If you too like this style, aim for similar ease in the front and back, no waist shaping, and little to no positive ease at the fullest part of the bust.
More about Fiona and her sweater
Fiona is a prolific and incredibly skilled knitter, and I was incredibly grateful for her feedback during this test. In fact, after she completed her sweater and we talked about the fit, I went back and completely regraded the sleeves. She knit her sweater in Garnstudio DROPS Cotton Light, which is budget-friendly and sensory-friendly. If you'd like to see more of her portfolio of work, you can check her out on Ravelry!
More about FBAs (including some hot takes!)
Ysolda - "How to choose what size to knit from a sweater pattern", here. Also, you're probably sick of hearing me say it, but her book Little Red in the City is THE ONE.
Cocoknits - "How (& Why) to Work Bust Darts, here (maybe you're beginning to sense how contradictory the advice is!).