How To Design Set-in Sleeves

A set-in sleeve allows a garment to fit the body closely with minimal extra fabric to interfere with fit or manifest itself in unsightly folds. The dimensions of the sleeve cap are determined by those of the armhole; here, I will demonstrate how a properly fitted cap is drafted for a handknitted garment using the armhole measurements. I have simplified the process of drafting the cap by using the same shaping on the front and back armholes and a symmetrical cap. When you compare the shapes of a sewn bodice and sleeve cap for use with woven fabrics to those of a knitting pattern, you will notice that the sewing pattern’s curves are more complex, with the armhole and sleeve cap shaped differently on the front and the back of the bodice.

Even if you compare sewing patterns intended for jersey fabrics to a knitting pattern schematic, you will usually find the sewing pattern to be more complex. The primary reason for a knitting pattern’s relative simplicity is ease of reproduction. Because the shaping is written out and the fabric created row by row at the same time that the garment’s shape is determined, a simpler shape allows knitters to focus on the fabric being created and the act of creating it. Luckily for us, because knitted fabric is stretchy and molds to the wearer’s curves, what is lost when the pattern is simplified is mostly gained back by the nature of what is being created.

For the purpose of this article, I will assume that we already have the body of a standard-fitting sweater with 2–4″ of positive ease in the bust in a 36″ finished bust. The armhole is 7.5″ deep, and the armhole seam is at the natural division between the torso and the arm (the break point). I will demonstrate how to draft the cap based on this armhole’s measurements (for a very close-fitting bodice with negative ease, you would draft the sleeve somewhat differently). This armhole is shaped the same on front and back, as most knitting patterns are. I am assuming a gauge of 24 stitches and 32 rows = 4″; 6 stitches per inch and 8 rows per inch.

Tools you will need:
• Large piece of paper (graph paper is useful but plain paper will do)
• Pencil and eraser
• Flexible ruler or measuring tape
• L-square ruler or wide rectangular ruler
• French curves or tailor’s curve
• Calculator with square-root function or a spreadsheet program

Step 1: Draw the armhole

set-in sleeve

Draw the armhole to scale. Do this even if you have already knitted the body, because you will need to be able to draw the sleeve on top of it. In my example, the armhole is 7.5″ deep. I need to find the measurement of the armscye (the measurement of the entire curved edge of the armhole). In order to do this, I can either measure around the armhole with a flexible ruler or tape, or I can do some basic math and figure it out. I will show you how the basic math works; doing so clarifies where the measurement comes from. Because this armhole is shaped the same way on front and back, I can find the measurement for one side and then double it for the whole armscye. The armhole shaping consists of binding off some stitches at the underarm, then decreasing some stitches over a certain length, and finally knitting straight until the armhole is the desired length.

Underarm bind-off: Divide the number of stitches bound off by the stitch gauge per inch. I bound off 8 stitches = 1.33″.

Decreases: I decreased 7 stitches over 15 rows (first decrease row plus every right-side row five times and every 4th row once). I need to find the hypotenuse (c) of the right triangle formed by the width of the stitches decreased (a) and the height of the rows worked (b). For this, I use the Pythagorean Theorem.

Step 2: The Pythagorean Theorem

Because I want to know what c is, first I must solve the equation for c.
c2 = a2 + b2
c = √(a2+b2 )
A is 7 stitches, or 1.17″. B is 15 rows, or 1.88″.
c = √(1.172+1.882)
c = √(1.37+3.53)
c = √4.9
c = 2.21″

Straight section: The total armhole is 7.5″ or 60 rows. I have accounted for 2 bind-off rows and 15 rows of shaping (17 rows), so there are 43 rows remaining, or 5.38″. On one side, the armhole measures 1.33″ + 2.21″ + 5.38″ = 8.92″. Multiply that by two to get the entire armscye = 17.84″.

Step 3: Draft the Cap

Cap height: On top of your armhole drawing, draw a vertical line, beginning at the bottom of the armhole (1) and touching the side of the front armhole. The height of the line is one third of the armscye measurement, minus a quarter inch (minus an eighth of an inch for bust sizes larger than 38″). The height here will be 17.84″/3 – 0.25″ = 5.69″. I will round it to 5.75″ to draw it. Mark the endpoint (2). Square across (draw a perpendicular line) from this line.

Mark a point on the cap height line at one quarter of the height (3). At 3, mark a matching point at the same height on the armhole (3a). Measure the distance from 3a to the top of the armhole (4). This example measures 6.06″: you have three quarters of the 5.75″ high cap (4.31″) from 4 to 2, and 1.75″ remaining at the top of the armhole from 2 to 4. If a significant portion of the shaped part of the armhole comprises this line, just measure it instead of calculating in this way because it will be slightly longer than just the vertical measurement—in this example, it’s insignificant. I will round it down to 6″. Do not add any ease to this measurement. (In drafting a sleeve for a woven fabric, you would add about a half inch of ease.) Now, take a ruler and place the 6″ mark (or whatever your measurement is) at 3 on the cap height line, then angle the ruler across to intersect with the line squared off from the cap height line, so that the end of the ruler touches the line. Mark point 5 at the intersection and draw a line between 3 and 5 (shown in green).

Mark point 6 at the center underarm. Now, look at the segment of the armscye from point 3a to point 6. Duplicate and reflect this segment from point 3 to new point 7. Basically, you are creating some shaping at the beginning of the sleeve cap (shown in pink) that exactly matches how you shaped the beginning of the armhole. (For an armhole that is more off the shoulder, with a wider sleeve and shallower cap, you would want this section to be flatter and wider than the matching armhole section, but for this example’s proportion duplication is a great rule of thumb.) You have also just determined the width of the upper sleeve—square down from 5 to the base of the armhole, then draw a line across to 7. This is half of the sleeve width, 6.75″ here. In this example, the sleeve will be 13.50″ wide.

In order to create a nice smooth curve for the sleeve cap, you will need to plot a curve around the green line drawn from 3 to 5. Two-thirds of the way up the green line, mark point x. Square out from x 0.75″. Draw a curved line (shown in orange) from 5 to 3 with a tailor’s curve, touching the line you just squared out. The curve adds as much ease as necessary to the sleeve cap. You will see that the pink and orange lines are now creating the outline of a sleeve cap that fits this armhole. Because the armhole is the same on front and back, the sleeve cap will be as well. Now, all that remains is to create the instructions to knit this sleeve cap, with the same shaping on both edges.

Step 4: Create Knitting Instructions for the Cap

The sleeve cap is 5.75″ tall. At my row gauge, that is 46 rows. I also have determined the sleeve width—13.50″, or 81 stitches. I will bind off the same number of stitches at each underarm as for the body (8 stitches)—65 stitches remain. There will be a section at the top of the cap that is bound off straight across (the drafted lines show more of a shallow curve at the top, but a portion of this curve is usually translated to a straight bind-off at the top). I will bind off 13 stitches at the top, or 2.16″.

The number of stitches I must decrease or bind off on each side is (65 – 13)/2 = 26 stitches on each side. I have 44 rows remaining in which to do this (46 rows of cap minus 2 bind-off rows at the underarm). I can decrease 1 stitch at each side on the next row and on every right-side row 17 more times, then work one wrong-side row even—18 stitches decreased on each side over 36 rows; 29 stitches remain. Recall Step 3, where you reflected the portion of the underarm decreases on the body onto the bottom of the sleeve cap; I have kept the same shaping here because I began with every-other-row decreases. Next, I will bind off 2 stitches at the beginning of the next 8 rows—8 stitches bound off on each side over 8 rows; 13 stitches remain. The remaining 13 stitches are bound off straight across.

Step 5: Check the Measurements

You must check the measurement around the perimeter of the sleeve cap to make sure that you preserved the correct measurement when you transferred your drawing to knitting instructions. Once again, use the Pythagorean Theorem. I recommend working in a spreadsheet because you can copy and paste the formulas and enter new gauges for future use.

Divide the sloped side of the cap into two triangles, one for each shaping rate (decreases and bind-offs). Find c of each triangle:

Pink Triangle:
c = √(a2+b2 )
c = √(32+4.52 )
c = √(9+20.25)
c = √29.25
c = 5.41″

Blue Triangle:
c = √(a2+b2 )
c = √(1.332+12 )
c = √(1.77+1)
c = √2.77
c = 1.66″

Find the width of the bind-offs at the underarm and at the top of the cap:
Underarm: 8 stitches = 1.33″
Top of cap: Divide the 13 stitches in half for 6.5 stitches = 1.08″
Add all of these elements together:
1.33″ + 5.41″ + 1.66″ + 1.08″ = 9.48″
Multiply by 2 for the entire perimeter: 18.96″

The armscye is 17.84″, so there will be 1.12″ extra on the sleeve cap to ease in when setting in this sleeve, or 0.56″ on each side. I find this amount to be perfect, because it’s small enough to take in simply without it looking obviously gathered. Having that little extra makes it easier to fit the sleeve cap into the armhole without constant adjustment, and it looks very nice upon finishing. However, if you prefer no ease in the sleeve cap (such as you would for a very close-fitting garment with negative ease), you may remove it by making the cap a bit shorter or the sleeve a bit narrower. Remember back in Step 3, when you measured from 4a to 5, and I said not to add ease to that measurement? If you had added the approximate half-inch that is normally added for wovens, you would have had about 2″ of ease in the cap, which is excessive for a knitted garment. Most importantly, be sure to never have less length around the cap than you have on the armscye because your sleeve will be ill-fitting and will bind around the armhole. If you make this error, congratulate yourself for working the garment in pieces and be glad that you can simply undo the top of the sleeve cap, add a few rows, then sew it back in.

This article was originally published in Interweave Knits Summer 2016.

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