Those of you who've been with us for a while know that we recommend using your upper chest measurement to choose your size. Here's everything you need to know!
What is the upper chest measurement, anyway?
The upper chest measurement is taken across the chest over the breasts, at a diagonal angle under the arms, and flat across the back.
At its core, upper chest is a measure of the size of your torso.
Why does upper chest matter in knitting?
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 not a good predictor of your frame size.
When we fit garments, it's important to fit from the top down. Because garments hang from the shoulders, then down through the underarms and across the top of the torso before even reaching the underarms, it's important to fit those measurements first.
Note: Check out the illustration above - that full bust line? It's in the lower torso. We're so used to thinking about our busts as being at the underarm because in knitting, we usually reach the full bust stitch count at the underarm. But it's not - it's beneath the underarms. Full bust is a lower torso measurement.
Instead of asking knitters to choose a size based on their underarm depth (armscye), shoulder width, and neck width, we can instead look at upper chest. Upper chest is a good predictor of those measurements because it measures the torso size. It's also a heck of a lot easier to measure your body's circumference there than it is to accurately measure your shoulder width and armscye without help!
Put another way, sweater fit depends on your armhole depth, shoulder-to-shoulder width, neck width, rib cage 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!
Here's a quick visualization if that's not clicking - at the end of the day, we take off our bras, and our full bust measurement instantly changes. But we have not changed size!
Caveat! 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?
If the pattern includes upper chest sizing recommendations
Designers are increasingly providing sizing recommendations based on your body's upper chest circumference. In my patterns, I recommend you start by choosing the size closest to your actual upper chest body measurements. Review the schematic, and make sure you are happy with the fit you'll get through the underarm, across the shoulders, and across the neck.
If the pattern only includes full bust sizing recommendations
If the pattern doesn't give you upper bust measurements, you have two choices.
First, consider how other sweaters have fit when you relied on full bust sizing. If your sweaters have been sloppy, with wide necks and deep armholes and overall just too much fabric, consider going down a size. If your sweaters have had tight armholes and strain across the top of your rib cage, consider going up a size.
Or, you can get more cerebral with it. Use an existing size chart, like Ysolda Teague's free size chart for women, which includes upper chest. Find your upper chest measurement, and look at the top to see how big your bust is expected to be for your upper chest measurement. Look at the pattern and see how much ease is recommended, and add that to the predicted bust size. Choose that size.
Example: Let's say my bust is 44" and my upper chest is 39.25". My pattern only tells me to choose a size with approximately 10" of positive ease, and has finished full bust measurements of: 39.5 (44, 48.5, 52, 56.5)(60, 64.5, 68, 72.5)”.
If I follow the guidance, I'll add 10" to my full bust of 44", and choose between sizes 4 and 5.
Instead, I'll see that for my upper chest measurement of 39.25, I'm expected to have a full bust of 40". I'll add 10" to that instead, and make a choice between sizes 3 and 4. Since I know that I'm busty, and since I grabbed these numbers from a popular drop shoulder design with a very relaxed fit, I would probably choose size 4.
Review the rest of the schematic
Choosing a size is always an art. Even if the designer makes a recommendation, you might not like the fit you'll get in the size indicated. I suggest reviewing the fit you'll get in the key underarm and shoulder measurements to make sure you like the base size.
Once you've settled on your base size, you should evaluate other fit points to see if you'll need a modification. If you follow this methodology, you may not end up with the same amount of ease at the full bust as the designer recommended. In my example above, choosing size 4 will give me 8" instead of 10".
Because our bodies get rapidly wider from the underarm to the bust, and then narrower again to the underbust, we are only our widest measurement briefly. Knitting stretches, and generally, a standard fitting sweater will be just fine with up to one inch / 2.5 cm of negative ease at the full bust - even if the designer recommends positive ease.
If you're happy and you know it...
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. Trust your judgment with sizing, and when in doubt, measure an existing sweater that you love and compare it to the schematic.
Plusses is your opportunity to knit up a DK weight, seamless raglan and to try out your size-picking skills. Because of the large stitch pattern, there are fewer sizes than my patterns would normally have.
By reviewing the size guidance, the schematic, and comparing your body measurements and that of another favorite sweater, you can fine-tune exactly how you want the sweater to fit. I like mine looser, but the armhole is deep enough that you can size down if you want to. Bonus? The schematic is available on the pattern page, so you don't need to buy anything to do this exercise.
Prefer a video on upper chest?
I have an IG highlight with demos on how to measure and answering some Q&A here.
We talked about this more in a One Wild Broadcast Episode.