Demystifying Yarn Substitution

With the variety of yarns available now, substituting yarn can be confusing—but it doesn't have to be. Make yarn substitution easier with these handy tips.

Lamb's Pride

The structure and fiber content of the yarn you use will affect the look of the finished fabric. This swatch is knit with Lamb's Pride, a wool and mohair singles yarn.

Photo by John Polak

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The Knowledgeable Knitter (Storey Publishing, 2014) by Margaret Radcliffe offers an in-depth tour of a sweater-knitting project to show the choices and options open to every knitter at every step. Radcliffe demonstrates not only how to execute these techniques but why you might choose one over another, allowing you to make tailored, elegant items that are beautiful reflections of your personal style.

Finding a Yarn Substitution for Your Pattern

You have the best chance of a successful garment the more closely you match the yarn used in the original design; however, you shouldn’t feel compelled to use the identical yarn. There are almost always appropriate yarns you can substitute. You just need to match the yarn’s three key attributes as closely as possible: these are the thickness of the yarn, the fiber content, and the yarn’s structure and texture. You should also consider the color of the yarn, but that’s more a matter of aesthetics and personal preference.

Understanding Yarn Weights

There are several systems for yarn weights in use. In the United States, the different thicknesses of yarn have traditionally been called by name, such as sport weight, worsted weight, and bulky weight. In the United Kingdom, the terms include 4-ply and DK (“double knitting”). The Craft Yarn Council has tried to standardize references to yarn weight for knitting and crochet using a numbered system that begins with size 0 for the thinnest yarns and ends with size 6 for the thickest. In all of these cases, the label refers to a range of yarns with similar thicknesses that may or may not be close enough to the thickness you want.

To check for a comparable thickness, you need to compare the yards per ounce (or gram or pound). If you are lucky, the pattern will provide yarn specifications that include how many yards or meters are in each ball or skein and how much each ball or skein weighs. Divide the weight by the length for the yarn you’re considering and compare the result to the original yarn. If one provides weight in grams and the other in ounces, you’ll need to convert them to the same units. After decades of doing these conversions, I have memorized that 1.75 ounces equals 50 grams. This is really all you need to remember. Or, if it seems simpler to you, 3.5 ounces equals 100 grams.

For example, the pattern calls for a worsted-weight wool yarn with 110 yards per 50-gram ball. You want to substitute a wool yarn with 198 yards per 100-gram ball. The easiest thing to do is to multiply the yards in the original ball by two to see how many yards would be in a 100-gram ball: 110 yards × 2 = 220 yards. The substitute yarn has only 198 yards in the same weight, so it’s a little thicker or denser than the original. A second yarn you’re considering is packaged with 225 yards in 4 ounces. To compare it to the original, you’ll need to figure out how many yards are in 50 grams. Remember that 1.75 ounces = 50 grams. Divide 4 ounces by 1.75 ounces to discover how many 50-gram balls are in 4 ounces, and you get 2.29. Divide 225 yards by 2.29 to get 98.25 yards in 50 grams, which is also a little thicker or denser than the original (which you’ll remember had 110 yards in a 50-gram ball). Are either of these yarns close enough to substitute? The answer is a solid maybe! You’ll need to test them out by knitting a swatch to see if you like the fabric when you are knitting at the correct gauge, but you also need to consider fiber content and structure, so read on.

When You Don’t Know the Yarn Specs

If your yarn is missing a label or the label doesn’t contain enough information, you can figure out what needle size would be appropriate by this simple test. Fold a strand of the yarn in half and hold it across the holes in a needle gauge. The hole that the double strand covers will indicate the needle size that will serve as a starting point. Knit a swatch with this size to see if you can match the gauge specifications and produce a suitable fabric. Adjust the needle size depending on your results: If you need to get more stitches per inch, use a smaller needle, which will make the fabric tighter and less stretchy; for fewer stitches per inch use a larger needle, which will result in a looser, stretchier fabric.

This also works if you substitute multiple strands of thinner yarn for a single thicker yarn. Twist the strands loosely together, then fold in half and lay them across the needle gauge. Stretch them a bit to prevent them from kinking up.

Fiber Content and the Finished Fabric

The fiber content of the yarn plays two roles. The density of the underlying fiber affects how much length there is for the weight at any given thickness, and the inherent properties of the fiber affect how it behaves. As an example, let’s compare cotton to wool. Sheep’s wool is less dense, with air trapped inside the cell structures of each hair. Most sheep’s wool used for handknitting is naturally crimped or waved. Cotton fibers are much denser, much shorter than the wool used for spinning yarn, and have no crimp.

The different characteristics of the fibers result in different yarn characteristics. Cotton yarns tend to be inelastic. They are usually more tightly spun than wool yarns, because more twist is required to hold the short fibers together so the yarn won’t fall apart. Wool yarns are more elastic because the crimp in the individual hairs stretches out straight when pulled and returns to its original length when relaxed. If you take two pieces of yarn, one cotton and the other wool, that are the same thickness and the same length, with the same number of plies and the same amount of twist, the cotton yarn will be heavier than the wool.

Because of these dissimilarities, garments knitted from the two fibers will also behave differently. Cotton garments, because they are heavier, tend to gradually stretch in length while worn. If they shrink in the wash, they will usually end up shorter and wider. Wool garments, because the yarn is elastic and less dense, hold their shape better. If they do stretch out of shape, washing restores the fiber’s natural crimp, and they can usually be blocked back to their original shape.

So, choose a yarn substitution with a fiber content that closely matches that of the original yarn. A wool and acrylic blend may substitute just fine for 100% wool. Nonstretchy plant fibers like cotton, linen, hemp, and bamboo can usually be substituted for each other. Silk, rayon, and other slippery inelastic yarns can also be substituted for each other. Less elastic animal fibers, like mohair, cashmere, and alpaca, can usually be substituted for each other, but depending on how tightly spun they are and whether they have been brushed to produce a fuzzy halo, their appearance and behavior can vary widely. And you can usually use all the nonstretchy yarns interchangeably. If the pattern calls for a 100% wool yarn, many times you can successfully substitute a wool-blend yarn that is at least one-third wool.

Generally speaking, any fiber you expect to stretch (anything heavy and inelastic, which includes anything that’s not wool) will perform better in a garment structured with seams to help support it. These fibers will also perform better the thinner the yarn and the less dense the pattern stitch. Fine yarn worked up into a delicate lace fabric will cause far less trouble than bulky yarn worked into a thick fabric.

How Yarn Structure and Texture Affect the Fabric

One of the surprising things about yarn is how yarns that have the same fiber content, the same thickness, and are the same color can look completely different in the knitted fabric depending on their structure. It’s obvious that fabric made from a fuzzy brushed mohair will look very different from fabric made from a smooth yarn. For this reason, it’s best not to take a complicated textured pattern stitch and knit it in a highly textured yarn, because the texture of the yarn will partially or completely obscure the pattern stitch. What’s not so intuitive is the difference in appearance that the ply structure and the amount of twist make.

The major difference is stitch definition. You can really see the stitch patterns in some yarns, and in others they can look like a disorganized jumble. In single-ply yarn, the twist of the yarn itself is very noticeable, making the individual stitches appear crooked because the fibers within the yarn are almost parallel to one side of the stitch and almost perpendicular to the other. The rounder the cross-section of the yarn, the better the stitch definition. The amount of twist also plays a role — loosely twisted yarns tend to have poorer stitch definition.

So, if there will be textured pattern stitches and you want to clearly see every stitch, avoid loosely spun 2-ply and highly textured yarns. If you will be working color patterns, keep in mind that using a fuzzy yarn will make the color changes less crisp and may obscure subtle stranded work, slipped-stitch colorwork, or intarsia altogether.

Excerpted from The Knowledgeable Knitter © Margaret Radcliffe, photography by John Polak. Used with permission from Storey Publishing.