A question I see pop up time and time again in knitting groups is: how can I do waist shaping on a sweater when there's no waist shaping in the pattern I'm using? How do I know how many stitches to decrease? And how often? (OK, that's technically three questions.)
In this blog post I'll guide you through what measurements to take and calculations to make to add custom waist shaping to any top-down sweater pattern, be it a pullover, cardigan, tunic, or dress.
Natural Waist vs. Preferred Waist
How do you find out where your waist is? You'd think the answer to this would be pretty self-evident but it's actually a bit more nuanced than first would seem.
I recently stumbled onto a wonderful sewing book that addresses different fit issues and how to alter your pattern to overcome them: Fast Fit: Easy Pattern Alterations for Every Figure by Sandra Betzina. Even if you're not a sewer, this book has a great section on how to measure your body to make a custom size chart based on your own measurements. That's really valuable information for fitting knitting patterns, as well.
In her book, Sandra Betzina instructs you to tie a piece of string or elastic around your mid-torso, then bend from side to the side as if doing the "I'm a little teapot" dance. The point where your mid-torso naturally hinges (and where the elastic travels to) is called the natural waist.
What might surprise you is that natural waist may not be the same as the narrowest point on your mid-torso. In her blog post about the representative size chart, Kim McBrien Evans writes that many knitters prefer using a point slightly above the natural waist — she calls this the preferred waist measurement.
For some people the narrowest point on the waist might be at the bottom of the rib cage; for others is might be located at the belly button level. Calculating waist shaping using the narrowest point as the waist measurement gives a more slimming look than going with the natural waist.
The beauty of making garments for yourself — whether they be knitted or sewn — is that you get to choose where your waist is. It might even vary from garment to garment. When fitting sweaters for myself, I like to use the narrowest point as my waist measurement. Whatever you choose, be consistent: measure the waist circumference and underarm-to-waist length at the same point.
For the first dozen or sweaters that I did, I always did waist shaping at the sides of the garment, placing two markers at each underarm and then working shaping at two sides of both markers. On every waist-shaping row, you're decreasing/increasing four stitches, that is, there are four shaping points per row.
But you don't have to limit yourself just to side shaping. In fact, some designs might make it difficult to place decrease/increase points at the underarms. For example, in my sweater pattern Hygge Days, the whole back piece of the sweater from one underarm to the other is occupied with a lace pattern which would be interrupted with shaping. To circumvent this issue, I placed waist-shaping only on the front of the sweater, about one third of width in from each side — I call this princess-seam shaping. This creates shaping akin to fisheye darts in sewing patterns. Similar to side-shaping, front-only princess-seam placement also decreases/increases four stitches per row.
I've used princess-seam shaping in other designs, as well. For example, in Tulip Route, markers are placed on both the front and the back at approximately one third in from the sides. Decreases/increases are made at both sides of the four markers, meaning there are eight shaping points per row.
You can also combine side and princess-seam shaping. In Emerald Chain, for instance, there are four shaping points at the underarms and additional four on the two sides of the mid-back for sway-back shaping. In Honung, decreases are first worked at four points (at the sides), then at six points (sides + mid-back).
Waist-shaping placement always goes hand in hand with the number of shaping points. The number of these points is usually the same for both the decrease and increase portions of the shaping. Oftentimes you've already placed markers at certain points in the work so it's very convenient to continue using those same points. But you don't have to!
For certain designs it might make more sense to deviate from this. In Maypop Hoodie, for instance, there are six decrease points: two at the right underarm, two at the left, and two on the back on both sides of the central lace panel. For waist-shaping increases, though, I omitted the increase points on the back as this would've created a flared peplum of fabric (like on a fishtail parka) right on top of your bum. This left only the four increase points at the underarms.
If your body is proportional, meaning that your bust and hips are roughly the same size, you can have the same number of decrease and increase rows. This creates a symmetrical, hourglass-like shaping on the garment. This option might be the easiest to start with when you're calculating your own waist shaping.
But, again, this doesn't have to be the case. Your figure and garment silhouette dictate the ratio of decrease rows to increase rows. For instance, if your bust circumference is smaller than your hip circumference and/or you're making an A-lined garment, you'd have more increase rows than decrease rows (see Dilaila's Hoodie and The Comeback Cardigan).
Conversely, if your bust is wider than your hips and/or you're making a cropped sweater than clings to your waist, it makes sense to have fewer increase rows than decrease rows. In some cases, there might not even be enough space for any increases at all! That's what I did on Golden Assam.
Before actually calculating waist shaping, you'll need a couple of key measurements of yourself, some important pieces of information from the pattern, and a few other variables. To take the measurements, put on the undergarments you intend to wear with the sweater. It's also a good idea to try on your in-progress project with sleeve stitches already separated from the body.
The measurements you need to take are:
underarm-to-waist length (measured from the garment underarm)
Check your pattern to find these numbers:
number of stitches at bust (after dividing body and sleeves)
body length from underarm to hem
the length of hem ribbing (and/or other edge treatment)
And make a decision on these:
length to work even at underarm
number of shaping points
How to Calculate Waist Shaping
Finally the fun part: math! For the waist-shaping calculations below I'm using the Fervent I knit a couple of months ago as an example. In this sweater, I decided to make princess-seam shaping, placing two markers on both front and back in equal distances from the underarms. Therefore the number of shaping points is eight.
The calculations below apply to both garments worked in the round or flat in rows. For the sake of brevity, I'll refer to rows in the instructions. If working on a garment in circular knitting, replace the word "row" with "round". The calculations are done in metric units.
In my example pattern I have:
number of stitches at bust: 192 sts
body length from underarm to hem: 40 cm
hem ribbing: 3 cm
stitch gauge: 22 sts per 10 cm (2.2 sts/cm)
row gauge: 28 rows per 10 cm (2.8 sts/cm)
And I'm choosing the following:
waist ease: 5 cm
hip ease: 5 cm
length to work even at underarm: 10 cm
number of decrease/increase points: 8
Let's start with the obvious one: stitches at the waist. As discussed above, decide where your waist is and measure the circumference around this point. Add your desired ease at the waist to this number.
Depending on the fit you're going for, the amount of ease may be the same throughout the garment… or it might differ. I usually like to allow for more ease at the waist compared to bust or hip, for instance, 5 cm (2") at bust but 7.5–10 cm (3–4") at the waist. In her recent article on ease on the Interweave blog, Kim McBrien Evans suggests 7.5–12.5 cm (or 3–5") of ease at the waist to allow for room to breath, twist, bend, sit, and stand.
In this case the yarn was pretty stretchy and I wanted the sweater to be quite fitted so I picked the same amount of ease for bust, waist, and hip: 5 cm.
# of waist stitches = (waist circumference + waist ease) × stitch gauge
In my example sweater, the number of waist stitches is (76 cm + 5 cm) × 2.2 sts/cm = 178.2 sts. Don't be alarmed that this is a fraction. We'll refine and adjust this number below.
# of stitches to decrease = # of stitches at bust - # of waist stitches
For my sweater, the total number of stitches to decrease at waist is 192 – 178.2 = 13.8 sts. As this number is not evenly divisible by the number of decrease points (8), I have to decide whether to round it up (to 16 sts) or down (to 8 sts). I'll decide to go with 16, therefore the final stitch count at waist is 192 – 16 = 176 sts.
# of decrease times = # of stitches to decrease ÷ decrease points
In my sample sweater the number of decrease times is 16 ÷ 8 = 2, meaning I'll make a decrease row twice, decreasing 8 sts each time.
For the next phase of the calculations you'll determine how many rows you have to work with. Try on your top-down sweater project and measure the length from the garment underarm to your waist. (The garment yoke should hang a few centimeters or an inch or two below your actual underarm.)
Waist decreases don't have to start right after dividing body and sleeves. In fact, your sweater will probably fit better if they don't. This is what I mean by the length to work even at underarm: the number of rows to work on the body before starting waist decreases. This usually ranges from 2.5–10 cm (1–4") and, counter-intuitively, can be longer for smaller sizes and shorter for sizes on the larger end of the range.
Since the number of decrease times is only two, I can allow for more rows to be used up when working even. In this case I'm going with 10 cm.
# of rows for waist decreases = (underarm-to-waist length - length to work even at underarm) × row gauge
For my example sweater the number of rows I have available for waist decreases is (21.5 cm - 10 cm) × 2.8 rows/cm = 32.2 rows. Now we can put the stitch and row count calculations together.
decrease rate = # of rows for waist decreases ÷ # of decrease times
In my example garment the decrease rate is 32.2 rows ÷ 2 = 16.1 rows. Since I'm working on a sweater, this number can be rounded to the nearest whole number, 16. If working on a cardigan knit flat, you want to round it to an even number so that you can work shaping only on right-side rows. (In this case it'd still be 16.)
My final waist decrease instructions then are: work 10 cm even after dividing body and sleeves, then decrease a total of 2 times every 16 rows, decreasing 8 stitches on each decrease row.
The increase calculations follow pretty much the same logic. If you're working on a long tunic or sweater dress, calculate the increases to fullest point on the hip, then work the rest of the hem even.
# of hem stitches = (hem circumference + hem ease) × stitch gauge
In my Fervent, this equals to (86.5 cm + 5 cm) × 2.2 sts/cm = 201.3 sts. We'll refine this number the same way as above.
# of stitches to increase = # of hem stitches - # of waist stitches
# of increase times = # of stitches to increase ÷ increase points
In my case, the number of stitches to decrease at hem is 201.3 – 176 sts = 25.3 sts. I'm keeping the same number of shaping points (8) so I have to decide whether to round this down to 16 or up to 24. I'll pick the one that's closest (24): the final stitch count at hem is 176 + 24 = 200 sts. The number of times I need to increase is 24 ÷ 8 = 3 times.
To calculate the number of rows available for waist increases you first need subtract the underarm-to-waist distance from the total underarm-to-hem length. You also have to take into account any ribbing, edging, or other patterning at the hem because you want all shaping to happen above it.
# of rows for waist increases = (underarm-to-hem length - underarm-to-waist length - hem ribbing) × row gauge
In my sweater, the number of rows I have to work with is (40 cm - 21.5 cm - 3 cm) × 2.8 rows/cm = 43.4 rows.
increase rate = # of rows for waist increases ÷ # of increase times
Putting the stitch and row counts all together, the increase rate for my sweater is 43.4 rows ÷ 3 = 14.667… rows or, rounded up, 15 rows. Again, if working on a cardigan, you want to round this figure to an even number (14 or 16).
The final waist increase instructions then are: work even to underarm-to-waist length, then increase a total of 3 times every 15 rows, increasing 8 stitches on each increase row.
Waist Shaping for Bottom-up Sweaters
What if you're working on a bottom-up sweater instead? You can use the same formulas to do the calculations, remembering obviously that you'll decrease below the waist and increase above it. Increase rate becomes decrease rate and vice versa.
The only piece of information you don't have access to is where to measure the underarm-to-waist length from. Guesstimate this from the pattern to determine how low the yoke will hang on your upper torso.
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