ACK! Math!

A friend wants to participate in this baby blanket KAL (Knit-A-Long) which (assuming you use the same kind of yarn and needles they use, and your number of stitches and rows per inch is the same as theirs) will result in a baby blanket that measures 36 x 52 inches. Only she doesn’t want to end up with a baby blanket. She wants to end up with a much narrower rectangular shawl. She knows I write knitting patterns so she sends me what she’s got so far of the KAL pattern and wants me to cut the width down.

My first break is that even though the blanket uses a whole bunch of different stitch patterns, all the stitch patterns have a 12-stitch repeat.  For a finished width of 36 inches (36.36 inches, actually), the cast on is 200 stitches, but 20 stitches of that is border (10 stitches on each side), which leaves 180 stitches (15 repeats) that I can play with.

My next break is the way the pattern is written. You’re supposed to put markers 10 stitches in from each side (for your borders) and then after you slip the first marker, you repeat from * to the next marker, so the number of stitches you have on a row is immaterial so long as the number of stitches between the two markers is evenly divisible by 12 (12-stitch pattern repeat). So I don’t have to rewrite the pattern; she can knit it as written.

The tricky bit is coming up with the number of stitches to get the desired width in inches.  Assuming you can get gauge (22 sts = 4 inches), you divide the total number of stitches you are to cast on by 22 and multiply the result by 4 to get total width in inches. Show your work:  

(number of stitches to cast on) = (20 stitches for the border) + (number of pattern repeats x 12 sts per repeat) = (number of stitches cast on divided by 22 sts x 4) = total width in inches.  

  • 200 sts = 20 sts (borders) + 180 sts (15 x 12-st repeat) = 36 inches wide.
  • 164 sts = 20 sts (borders) + 144 sts (12 x 12-st repeat) = 29.8 inches wide.
  • 140 sts = 20 sts (borders) + 120 sts (10 x 12-st repeat) = 25.45 inches wide.
  • 116 sts = 20 sts (borders) + 96 sts (8 x 12-st repeat) = 21. 9 inches wide.

Hows that for 9 o’clock in the morning?  

But wait! When I was talking to my friend last night, we got to talking about knitting and math, and I was talking about the Savannah Squares shawl and figuring out how big to make it. It’s a square shawl meant to be folded on the diagonal and worn bib stile around the neck. I’ve already determined that I need a diagonal length of 52 inches (130 cm) for it to hang like it’s supposed to.

Since it’s being knitted “in the round” (i.e., outward from a center point), what I’ve been doing is measuring from the center point of the square out to one corner and doubling that measurement.

But then I realized: The corners of a square are 90 degree angles by definition. Folding the square in half on the diagonal to get a triangular shape makes that triangular shape an equilateral right (45, 45, 90) triangle. So if I want to know how long the sides of the square have to be to get a diagonal of 52 inches — wait for it — I take the pythagorean theorem(!), make C=52, and solve for A and B where A=B! And guess what? There’s an app for that . . . (It’s 36.25 inches/92 cm, BTW)

I also realized I’m going to Need More Yarn. . . . so after my MRI tomorrow, I’ll have to beetle over to Michael’s because they carry the Red Heart Unforgettable yarn, and hope they have 2 skeins of that colorway like their website sez they do.

Author: WOL

My burrow, "La Maison du Hibou Sous Terre" is located on the flatlands of West Texas where I live with my computer, my books, and a lot of yarn waiting to become something.

One thought on “ACK! Math!”

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