Math-Foo – recalculating for different gauge

I decided to knit a Steggie for my older son, Eliah. I just love playful clothes on kids, and knitting gives me the opportunity to create something fun and unique. Unfortunately my brain sometimes does stupid things. Like buying DK yarn, when the pattern, in fact, calls for Aran weight yarn.

I could have bought a different yarn, and saved the DK stuff for later, but I think I need to momentarily stop buying yarn and actually produce something with what I have. After two large yarn splurges my boxes and bins at home are full, and although I could buy more bins, there’s also the ambition to actually do something with the contents, rather than just storing the yarn.

Said and done. I set out to swatching (yawn!). I did a few samples with the Sport Alpaca from Viking Garn. The label says 3.5 mm needles, but I’m a pretty tight knitter and often find myself having to go up one size. I tried 4  mm, and finally decided on 4.5 mm needles, which after some calculations revealed that I would get about the size I wanted (small) if I knitted after the XL instructions and 4.5 mm needles.

I did the calculations with the 4 mm sample, and here’s the math for it.;

  • Find out how many rows per cm you knit (X)
  • Find out how many stitches per cm you knit (Z)
  • Find out how many rows the pattern calls for per cm (Y)
  • Find out how many stitches the pattern calls for per cm (S)
  • Calculate conversion rate for stitches. This is the important one because the width is hard to measure afterwards, and this will tell you how many stitches to cast on. The formula is as follows: Z / S = conversion rate. In my case the pattern calls for 1.8 stitches per cm and I’m knitting 2.4 I get 2.4 / 1.8 = 1.39.
  • Calculate conversion rate for rows: X / Y = conversion rate. So if Steggie calls for a row count of 2.4 rows per cm, and I knit 2.8 the conversion rate becomes 2.8 / 2.4 = 1.17. This number, can be used, if the pattern tells you to things on row x. If nothing else, you can use it to double-check the figure and see if you’re still on the right track.
  • Finally, if the pattern tells you to cast on X stitches, you just multiply this with the conversion rate – in this case 56 x 1.39 = 80.62.

The largest size called for 72 stitches, so I decided to go up to needle size 4.5 mm, which was close enough. I knitted a small sample to make sure that it still looked good, and to double-check my assumptions, and the measurements added up.

Steggie is a really fast knit (but the zipper will take a while, I’m guessing, especially since I’ve never added a zipper in handknits before) so I’ve already done the two fronts and a back. And measuring those, I’m right where I need to be for the size I’m doing.

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3 Responses to Math-Foo – recalculating for different gauge

  1. Thank you for posting this formula. I am keeping it for a time when I will more than likely need it. 🙂

  2. Pingback: Eliahs Steggie | The everyday life of a nerdy knitting junky

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