Unraveling the Needle Size Mystery: What Size Knitting Needle Should I Choose for Alpaca?

I once edited a book that included a hat knitted in bulky baby alpaca yarn. The hat was popular, and we got several calls from knitters asking about an error in the pattern. The designer called for size 7 needles and 5½ stitches per inch, and the yarn label called for a size 11 needle and 3 stitches per inch. Surely we must have made a mistake—the designer couldn’t have knitted the hat on needles so small? But knit she did, and the yarn made a firm but lovely ribbed fabric.

Another time, a designer submitted a swatch using a fluffy discontinued alpaca/silk yarn that the manufacturer called a DK-weight. I assigned a wool yarn described as fingering-weight and was confident that the new gauge would be the same or smaller. But the designer wrote to say that the new yarn was much bulkier than her original swatch; she'd had to go up several needle sizes and change the pattern to omit several repeats. Later I asked the wool yarn’s manufacturer whether she thought the yarn should have been labeled as sportweight, and she shrugged. “I like it on smaller needles and a tighter gauge, so we call it fingering weight,” she explained.[PAYWALL]

A wide range of gauges

The label for the Blue Sky Baby Alpaca sportweight yarn in the Timberlane Cowl lists the needle size as 3–5 (in the United States needle classification, or 3.25–3.75 mm). The four swatches above are worked on (counterclockwise from top left) sizes 7, 4, 2½, and 1 (4.5, 3.5, 3, and 2.25 mm) needles. The size 4 needle used in the cowl pattern makes a fabric that is neither floppy nor rigid, but a swatch worked on size 2½ needles is still lightweight and flexible, appropriate for a cowl or scarf. Even going down to a size 1, the fabric feels relaxed, not hard, good for a hat. Going up to a size 7, the fabric gets a bit floppy.

Millspun yarns generally include some indication on the label as to what needle size to try and what gauge is expected, but these numbers are more or less subjective—and that's before we get to the basic truth that some knitters just produce looser or tighter fabric on the same needles. But if those recommendations don’t necessarily give you solid advice, what can you rely on? And what if you've lost the ball band or picked up a one-of-a-kind skein?

You’re going to say swatch, aren’t you . . .

Well, yes.

Yes, but longer . . .

There are a few ways to help figure out where to start. One of my favorite tricks for narrowing down the right needle size is to fold over a length of yarn and push it through the holes of a knitting needle gauge. When you find a hold that's not too loose and not too tight, start swatching using the corresponding size needle. (See "How to Knit with Mystery Yarn.")

Another source for clues about your yarn is other skeins of yarn that you've already worked with. You can compare the sizes of two yarns by looping them together and running your fingers over the join. Is your yarn of inquiry thicker, thinner, or similar? Use what you know of the control yarn to make an educated guess about what needle size to start with.

To compare the grist of two yarns, interlace them and roll the join between your fingers. It’s easy to tell which one is thicker or denser. Photo by Matt Graves

And always remember that just because you can get a certain gauge with a certain yarn doesn’t mean you should. If you knit a worsted-weight yarn on size 1 needles, you may wind up with a scarf firm enough to stand up on its own. Swatching is your chance to find out not only if you can get the required gauge but also if you like it.

Yarns on the surface

The Blue Sky Baby Alpaca yarn shown here is not tightly twisted. (It doesn’t need to be, because the long alpaca fibers don’t need a lot of twist to secure them in the yarn without drifting apart or pilling.) It has a soft surface, not a full-blown halo but not crisp or slick, either. That surface can bloom in an open fabric or squish down in a tighter gauge. Yarns with a halo that squish down between your fingers can be worked in a looser gauge, if you like, because the fibers may fill in the space between stitches.

You may find that there’s a narrower range of needle sizes and gauges for some yarns. Superwash yarns have been treated to remove or stick down the scales on the wool follicle, so their surface won't bloom the same way an untreated yarn can. The same goes for mercerized cotton, whose shiny surface has been smoothed by removing little cotton fibers. Silk is naturally smooth, and even if silk yarns haven't gone through a chemical treatment, they're also not likely to “bloom in the stitch.”

On finishing

You’ve probably noticed that some yarns and swatches grow bouncier when they’re washed, tugged into shape, and allowed to dry. You may never have tried to give a knitted piece a fulling finish—where you immerse it in hot water, rough it up a little, and give it a squeeze—but this can make the fabric even more cohesive and fill in spaces between stitches.

Depending how your yarn has been treated before it gets to you, there may be some residual spinning oils or other treatments on the surface that come out in the wash. When these rinse away, your yarn may fluff up and change character. (Some knitters choose to wash their yarn before knitting it up, especially if it’s come on cones.)

For these reasons, you really want to not only swatch your yarn, but also wash your swatches the same way you plan to wash your finished item. Tie knots in the cast-on tails, work purl stitches, or duplicate stitch on your swatches corresponding with the needle size, and you'll be able to tell which needle created the fabric you like best.

This can all sound like a big hassle when all you want to do is cast on your exciting new yarn in an exciting new project. Depending on what you’re making, it may not be essential to do all this preparation; after all, a scarf or shawl will probably work just fine in a close-enough gauge. But for a one-of-a-kind yarn that you’ll wear forever, a little needle-size detective work is worth it.

-Anne