Set in a sleeve like a pro.

Anyone who has read my books or taken a class with me (and possibly anyone who has been within 10 miles of me) knows that I’m pretty much a fanatic about sweaters done in pieces, and the fit precision you can get with set-in sleeves in particular. I think seams are magical things, transforming this stretchy, sometimes unwieldy, with-a-life-of-its-own fabric into a structured and well-fitted garment.

The number one response I get when I voice this opinion, though, is that lots of knitters hate setting in sleeve caps and think they never come out right.


So, I thought I’d share how I do them. I took some snapshots of the seaming for my Rowan Options KAL sweater so that I can walk you through my process.

Background on Caps.

Before I get started, let’s start with a visual of how things should work. At least to the level of precision that you’ll be able to feel with your hands, sleeve cap seaming works if the distance around the armhole edge is the same as the distance along the curved part of your sleeve cap:

sleeve-cap-drawing-identical lengths

(Okay, okay. They’re not exactly the same. But unlike in sewing, your fingers shouldn’t be clever enough for the difference in length to be at all troubling – or even noticeable.)
This means that if you’ve messed with the length of either of those edges (say, by increasing the width of the bicep, or by not matching the designer’s row gauge), your sleeve caps probably won’t fit. If that’s the case, I strongly suggest ripping them out, re-calculating the sleeve cap shaping so that they’ll fit, and then trying to seam. There should be no “easing in” of the sleeve cap, here!

Step one: Seam the shoulders.

I like to use regular old mattress stitch for all of my seaming. I think it’s sturdy, attractive, and produces a seam that’s not too bulky.


After seaming the shoulders, I suggest laying your sweater out on a table the first time you pin.

Pinning is everything.

The single biggest and most important thing you can do to make your sleeve cap set in well is pin it properly.
By pinning the cap in properly, you’ll be able to

  • tell right away if the sleeve cap won’t fit in the armhole,
  • identify any bunching or mistakes before you start, and
  • enter the process knowing it will work, which helps make the whole thing less anxious.

I strongly prefer lockable stitch markers with pointy tips for this, because I can place the shaft of the pin exactly where I’ll seam, rather than mashing the knit pieces together.

Place your first pin at the shoulder seam. Hand-knit sweaters are typically written with symmetrical armhole and sleeve cap shaping, where the front and back of the garment are the same. So the shoulder seam itself should get pinned to the exact center of the top of the sleeve cap, like this:


Place your next two pins where the bind-offs stop. The first set of bind-offs on your sleeve caps and armhole edges (and probably the second set of bind-offs too) should match exactly. You’ll be horizontally seaming those one stitch to one stitch. So, pin together the exact spots where the bind-offs end, and the decrease-based-shaping begins.


When you’re seaming, these pins tell you to pay attention and switch what you’re doing.

Next, match your straight edges at the top of the cap.

I like to match the easy, straight edges of the cap next. The shoulder area on the body and the top bind-offs of the sleeve cap are nice straight lines. So I pull them up nice and snug next to each other:


And then place one pin at each end of that straight section:


You’ve now pinned together all of the straightforward bits.

Tackle the curves.

Now, you’re at the part where the armhole edge is shaped a little differently than the cap edge. Typically, the cap edge will have more shaping, and less height; the armhole edge will have more height, and less shaping. But the length of the edges should be essentially the same – that is, you should be able to match them like this:


And once you have, place a couple of pins (every inch or so?) along this edge.


You’re now finished pinning!

Check your work.

The best time to identify any lumpiness, errors in pinning, or any other problem is before you pick up your tapestry needle. At this point, I strongly recommend shaking out your sweater and laying it down flat.


If things have gone well, the sweater will look nice and flat. If you see any problems, un-pin and re-pin until it looks right. If you can’t make it look right, now’s the time to fix that by re-knitting your sleeve caps.

Seam it up!

Now, it’s time to seam – I use mattress stitch because just like with the shoulder seam, I think it makes for the cleanest, least-bulky, strong joining. I work about an inch of mattress stitch at a time, loosely, and then pull everything snug. Repeat carefully all around the sleeve cap.

I find videos to be not tremendously helpful for learning mattress stitch – watching someone else do it doesn’t actually help you figure out if you’re doing it correctly – but I did record a video for the Rowan Options KAL on how to properly seam your sweaters: Click here to watch it.

I have a few tips for the seaming process itself:

  • Take it slow – I did a quick poll, and most of us who seam sweaters regularly need at least 20 minutes for each sleeve cap. This isn’t something you’re going to whip together quickly before you do something else.
  • Use your pins. You’ve pinned it well – and you should use the information those pins are giving you. In particular, you should be reaching the pins at roughly the same time on both pieces. In other words, you shouldn’t get to the pin on the armhole edge side way before you get to the same pin on the sleeve cap side! If this happens, pick out your stitching for a couple of inches and try again.
  • Use strong, smooth yarn for seaming. In many cases, you can use the yarn you knit the sweater from. But if your yarn is nubby, or easily broken, or has a rough texture, or is bulky – use a smooth, strong, smaller yarn to seam with in a similar color. The yarn you use won’t be seen when you wear it!

You can also make your seaming somewhat simpler by working your shaping at least one stitch in from the sides – but that’s a different tutorial!