Design Theory Part 2: Measuring and Mathematics

(An aside: Guess who got bored and changed her layout? THIS GIRL.)

So if you missed it yesterday, there’s a brief tutorial on the very, very basics of algebra and a simplified example of how you may be using algebra in your knitting life already, but don’t even realize it. If the word “math” sends you into fits, you may want to breeze over that post while taking a deep breath and drinking an alcoholic beverage of your choice, if you are old enough to drink in your country (only responsible pandas around here, I assure you).

Last week, we talked about that dreaded “s” word, swatching. Today we’re going to walk through taking data from a swatch and turning it into usable information for designing. I was wrong in last week’s post about my gauge area—I was measuring over 2″, not 4″ (because I got sick of knitting my swatch and didn’t really have a good 4″ of usable fabric for measuring, oops). This is not really a big deal it just changes the way we’ll use some of the data.

Things that I know, based on my swatch:

My gauge, post-blocking, was 11.5 stitches and 19 rows over 2″.

Good to know, but I don’t use numerical data in 2″ increments. Just like I wouldn’t say 3 pairs of oranges; I would say six oranges. So I need to get the estimated gauge for 1″. (Just in case it’s not obvious, 1 goes into 2 two times, so I’m dividing by 2; if my gauge was over 4″, I’d divide by 4.)

11.5 ÷ 2 = 5.75 stitches per inch; 19 ÷ 2 = 9.5 rows per inch

We’re going to take that information and just hold on to it in the back of our brains while we sidetrack to get a little more information that’s not available from the swatch. A swatch is a representation of how a knitted fabric “should” look and feel like, in the end of the process, but that fabric has to fit on our bodies. I know that you’re looking at me like I’m an idiot right now, but stay with me. In order to make sure that we’re knitting to fit ourselves, we have to take some measurements. I highly recommend looking through Ysolda Teague’s Little Red in the City, as she provides exquisitely detailed instructions on what parts of the body to measure, how to measure them, and even a little fill-in-the-blank chart for you to list your own measurements (or the measurements of someone else, if you’re knitting as a gift).

Since I’m knitting this sweater dress for myself, I’m going to use some nice round numbers that are close to my actual numbers for this example (mostly because I don’t feel like measuring myself right now). First, though, I need to identify the measurements that are necessary. I would measure my bust, my upper arm, and my hip circumferences initially. Bust and upper arm are pretty self-explanatory, but I also want to make sure that the skirt is going to skim my hips the way I want, so I need that hip circumference number. Looking back at my sketch, I want this to have an empire waist, so I would also measure the length from my underarm to just below my bust (I think I measured about an inch below my bust).

Full bust circumference: 44″; arm circumference: 13″; hip circumference: 43″; length from underarm to underbust: 6″

Note: I used my full bust measurement and not my underbust measurement, because I didn’t want to have to work in bust shaping (the underbust measurement is smaller than the full bust measurement) and because I’m pretty sure seaming the body with the skirt will pull in the fabric a bit in the underbust.

I’m going to go more in-depth about the construction in another post, but as I mentioned in the comments last week, I’m actually knitting this from the “bottom” up (though I suppose you could argue it’s from the middle up and down…). Because I want a seam along the empire waist line and I’m a fan of decreasing rather than increasing (because I’m lazy and like to have shorter rows towards the end), I started first with the sleeves and then with the bottom of the upper body. More on that later, I just needed to explain that before we got to the math.

Let’s gather our facts: I wanted to start knitting with the sleeves. I have my upper arm circumference (13″) and earlier, I determined my stitches-per-inch number (5.75 stitches). I rounded up to 6 stitches per inch, because that’s just an easier number for math. Let’s look at what I need to know: How many stitches do I need to cast on in order to make my sleeves fit over my arms? As I talked about yesterday, a little bit of math, solving for what we need to know, will get our answer.

y = x * a, or the number of stitches needed for the arm = the arm circumference * the stitch gauge;
y = 13 * 6 (because I rounded up), or 78 stitches

I rounded up to 80 stitches, again because I like doing things in tens and I needed to give a little extra room since I rounded up on my stitch count. I also need to know the number of stitches that I’ll have to cast-on for the body portion, so using my full bust measurement, I worked my math like so:

y = x * a, or the number of stitches needed for the body = the body circumference * the stitch gauge;
y = 44 * 6 (notice it’s the same number; stitch gauge is stitch gauge), or 264 stitches

Here I went down to 260 stitches, again because of this weird thing with tens and because I had rounded up my stitch gauge. I want the fabric to be loose, with some positive ease, but not a ton.

There are lots of other numbers we could be looking at, but with this information, we can begin knitting and work out the other stuff when we get to that. Next week, we’ll look more at the construction of the sweater dress, as well as the beginning of the knitting. (This means more pictures and fewer numbers.)


8 thoughts on “Design Theory Part 2: Measuring and Mathematics

    • I’m glad this is making sense! I was a little afraid that there was too much going on; that’s why I’ve been breaking out posts. So much to discuss!

  1. Pingback: Design Theory 3: Construction « Threadpanda

  2. Pingback: Design Theory 2b: Do As I Say, Not As I Do « Threadpanda

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