Simple Knitting Math

I always did enjoy math and algebra but never thought about how I would use it in my knitting.  I’ve recently started to think about designing my own patterns, and have been using the same equations over and over.  Though this Math is simple, it would be even easier to write down the equations and save the time thinking about how to do the Math each time.  Following are some of the equations I keep using over and over, and their practical uses.  I will apply the numbers from a recent design project to help the equations make more sense.

  1. Figuring out how many stitches to cast on from knitted gauge swatch:  Figure out the size of the finished garment.  I was designing a cowl with a desired circumference of 21 inches.  My gauge swatch had 9 stitches per inch.  Therefore I needed  (21 x 9) or 189 stitches total.    [Number of desired inches x Number of stitches per inch= Total number of stitches needed].  In my cowl, I was using a cable pattern that was worked over 9 stitches.  Since 9 divides into 189 evenly, I ended up with 21 cable repeats.  If my total number of stitches had not been evenly divisible by 9, I would have added a stitch or 2 to the total to make an appropriate total number for the stitch pattern I was using
  2. Figuring out how to evenly space increases in the round: For my cowl, I wanted to start with a smaller number of stitches, and then evenly space increases on the last round before the cable pattern.  I planned the cowl this way because I know that cable stitches will cause the fabric to contract a bit.   I didn’t want to end up with an hourglass shaped cowl with the cable portion less wide than the edges, which I planned in garter stitch.  I decided to cast on only 80% of the total stitches needed, work the edge, then add on the remaining stitches in the last round before starting the cable pattern.  Since I needed 189 stitches for the cable portion, I would need to cast on (0.8 x 189 = 151 stitches), then add (189-151 = 38) stitches in the last round before the cable.  Since I would have 151 stitches on the needle. I would need to increase every (151/38) = 3.97 stitches.    [Current number of stitches / (desired number of stitches after increase -current number of stitches) = stitch interval to work increase].   I rounded this number to 4, knowing that after the last increase I would likely only have 1 or 2 stitches before the increase.  When you increase every 4th stitch, that means Knit 3, then increase on the next stitch.  After the 37th increase, I knit 1 then increased.
  3. Figuring out how to evenly space decreases in the round: After the cable section of the cowl was knit, I wanted to decrease back down to my original number of stitches to match the other edge of the cowl.  I already knew I had to decrease 38 stitches because I had added 38 stitches after the lower edge was knit.  Here is the equation I used to figure out how to space the decreases.  [Stitches on needle / (Stitches on needle-desired number of stitches after decrease)].  189/ (189-151) or 189/38 = 4.97.  I would need to decrease every 5th stitch.    I was planning to decrease by Knit 2 together.   To decrease every 5th stitch on Knit 2 together, I would need to Knit 3, then knit 2 together.  However, because my decrease interval is actually 4.97 and not 5, I needed to make an adjustment at the end of the round in order to get all my decreases done.  I accounted for this discrepancy by doing Knit 3, Knit 2 together 37 times taking me to 185 stitches.  I had 4 stitches left on the needle and 1 more decrease to do.  Thus I knit 2, knit 2 together for the last decrease.

I hope these simple equations help you.  I admittedly have learned some of this “the hard way”.  I hope I can save some of you from that more painful method of learning knitting Math.

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