The Knitting Fiend

“How To Use the Magic Formula” (or How to Shape a Knitted Sleeve.)

Some knitters working on the pure and simple knit-a-long are discussing adjusting the sleeve length when knitting top down. I decided to write a “How to shape a sleeve when knitting from top down” calculator. You can visit that web page and use its calculator whenever you are redesigning the lower portion of a sleeve. The calculator provides separate results for knitting in rounds or rows.

For those who want to understand how to do the calculations, I’ll explain. If you don’t want to understand, that’s ok. Once a calculator exists, it’s not absolutely necessary to understand. For today, don’t cross the line below. Just remember this discussion exists; return later if you ever decide you need to understand how to calculate shaping without using a program.

Oh, another thing! Many knitters working top down read reassurances that their gauge can be off a bit, and they don’t need to know their sleeve length etc. and they can adjust as they knit. This is kinda’, sorta’ true. The hitch is, you need to “design for uncertainty.”

How? I’ll tell you at the end of the article, since, logically, even if you skip my discussion about shaping, I need to refer back to it!

As before when I discussed increasing to taper a sleeve knit from the bottom up: those who want to cross the line, do so at your own risk! (Others can just skip over the portions between the horizontal bars.)

---

Now, I’ll apply the method I use to calculate sleeve shaping knit back and forth in rows and knit top down, by way of example. If this looks hauntingly familiar to those who read how to shape by increasing, it’s exactly the same example. Top down shaping is no different from bottom up shaping!

Suppose I want to increase from 20 stitches to 44 stitches over 30 rows, and the piece is shaped like sleeve similar to the one illustrated to the right. Here’s how I would calculate the shaping:

• First, I’m an engineer by training, so I always draw a sketch before doing math. See the schematic.
• I want to decrease from 34 stitches at the biceps to 20 stitches at the cuff . That is a total of (34-20)=14 stitches, or 7 stitches on each side. I put a “7″ on either side of the schematic.
• I want the stitch decreases to occur over 30 rows. To simplify shaping, I also want to make sure I only increase when the right side is facing (if I hand knit) or when the carriage is on the right (if I machine knit.) To force the decreases to occur only on odd numbered rows, I divide the number of rows by two and determine that 30 row / 2 = 15 pairs of rows. I labeled those values on the right hand side of the figure.
• Now, remember I want 7 decreases? Notice, how I placed 7 red dots for the decreases. Because this is a sleeve, I want to knit a few rows before the first decrease and a few after the last one. So, I sprinkled the dots away from the edges. Examining the figure, I notice I have 8 =7+1 “regions” around the decreases. I labeled the “8″ regions in green.
• Now, I’m going to figure out how many pairs of rows must be in each of those 8 regions. To figure that out, I first divide 15 pairs/8 regions and round down. That results in 1 pairs of rows in each region. This means each region has at least 1 pair of rows in it, but some may need 2 (that’s one more than 1.).
• How many of the eight regions need 2 pairs of rows? Well, when I divided 15/8, I found 15/8= 1 plus 7 left over. So, 7 of the 8 regions need an extra pair of rows. Meanwhile 1 region (= 8-7) has only one pair
• That’s as far as the magic formula gets me. At this point, I, as the all powerful designer, must decide which 7 regions will have 2 pairs of rows and which has only 1 pair. I could sprinkle around the 7 regions and 1 region however I wanted. I decided to make the very first decrease region have 1 pair of rows (that’s 2 rows), and all the rest have 2 pairs of rows (that’s 4 rows) . You’ll find the instructions at the calculator web page.
• Now, why don’t you repeat this exercise with the values you are going to
  knit? Compare your result to the one this page suggests. Notice that, since this is a program, I always put the regions with fewer rows between increase near the cufft, and the ones with a larger number of short rows near the underarm. You don’t need to do that. However, it has the advantage of making sure the sleeve is always at least as wide as necessary.

---

Now, designing for uncertainty! If you are knitting a sweater top down, by the time you start knitting the sleeve, you should know your knit and row gauge. But, maybe you don’t really know how long you want the sleeves to be? The thing to do when figuring the increase rate is . . .cheat.

The concept underlying the cheating is this: It’s ok if the sleeve is too wide just above the ribbing. You can always decrease stitches evenly across the row one round before knitting the ribbing. It will look fine! (In fact, this is the method Ann Norling uses in her directions for knitting a sweater top down.)

So, to cheat, add a few rounds when calculating the sleeve shaping. If you think you might want the sleeve 1″ longer than your current pattern suggests, and your row gauge is 6 rows per inch, add 6 rounds to the number suggested in the pattern. ( Or, you can add a few stitches to the area above the cuff instead.) When you knit, the sleeve will taper more slowly than in the original pattern.

As you knit, try the sweater on. When the sleeve is long enough to begin the cuff, stop knitting. Count the number of stitches; look up the number you need in the cuff, and just use on of my calculators (decrease stitches evenly across the row) to figure out how to space the decreases above the ribbing.

Now, remember these web based knitting calculators exist. When you decide to lengthen or shorten the sleeves in a published pattern, visit my blog (The Knitting Fiend). You don’t even need to find this article, I added buttons to the side bar; just look to the right. Click the one you want, and use it to figure the new shaping.