Substituting Yarn and Changing Needle Size (With Case Study!)

I recently released my second knitting pattern, the Slouchy Lace Hat. Because I’m still new to pattern design, I knit the hat several times before I felt confident releasing it to the world. Along the way, I was able to explore what happens when substituting yarn and how significantly changing needle size can impact the finished project. Today, I want to look at three of the samples I made as case study.

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Why Substitute Yarn?

I find that one of the most stressful parts about learning a new craft is finding and purchasing the right supplies. There are a lot of factors, both general and personal, that impact these choices. And often the answer isn’t “you can” or “you can’t,” but rather “it depends.”.

When it comes to knitting, most patterns specify what yarn is to be used. This is usually the yarn or yarns that the sample was knitted in. From a pattern writing perspective, this makes sense. Unless you test the pattern using the yarn, how do you know for sure that the finished object will turn out right? Even if the gauge is the same, will it have the same drape and coverage? It’s impossible to promise that without testing.

But in reality, people successfully substitute yarn all the time. The trick is knowing how (and how much) you need to adjust the other factors in your project to accommodate the new yarn.

The reasons for yarn substitution are many. Sometimes, you just can’t get the required yarn. Things go out of production, yarn stores only stock so much. You may want to switch to a less expensive yarn or use something already in your stash. Some people are allergic to wool or and vegans may not want to use any animal based yarns. Plus, a significant percentage of patterns are sold online as instant download PDFs, which means that your pattern could have been designed by someone living halfway around the world who has access to totally different yarns!

How Do You Substitute Yarn?

I start by analyzing the properties of the recommended yarn. Fiber content, yarn size, and yarn structure can all have a big impact on how the yarn behaves. If you’re new to knitting, I’d recommend sticking to substituting yarn used in any given pattern with something similar in fiber content, yarn construction, and yarn size.

The below information is intended as a general guide, however, there’s no way to guarantee success when swapping out yarns. I recommend making your best informed guess, then purchasing a single skein to swatch with before committing to a full project.

Fiber Content

In some cases yarns with different fiber contents can be swapped on a 1 to 1 basis with little to no changes. In others, the fibers act so differently that significant adjustments are required and the end project will drape and function very differently.

What is Fiber Content?

On every yarn you buy in a store, you should find a note with the fiber content. Think of these as the “ingredients” used to make the yarn. You might see “wool,” “Superwash Merino Wool,” or “Acrylic” printed on the yarn label. Some labels will list multiple fibers, something like “50% cotton, 50% linen” or “70% Silk, 30% Mohair.” Fiber content is important because different fiber types have different chemical and physical properties, which impacts how the end yarn feels, looks, and needs to be cared for.

What Fiber Types Can I Swap?

If you are looking at yarns that are constructed similarly and the same size, it’s usually possible to use a yarn with a different fiber content as long as the fiber contents are within the same basic category.

Wool, and many specialty wool fibers (cashmere, alpaca, etc.) can be used more or less interchangeably because they have similar chemical and physical properties. If you’re using wool, I’d also pay attention to whether or not the intended yarn is superwash. Wool that has been treated to be superwash will grow or stretch out a bit after wet finishing, while non-superwash will will “bloom” or fluff up a bit more and may shrink a small amount (especially if agitated too much during wet finishing). This will have an impact on your finished gauge, as well as the drape of your project.

Synthetic fibers like nylon, polyester, and acrylic get a little trickier. Nylon and acrylic are often made to mimic wool, and will knit up pretty similarly. So, you can often use them interchangeably. However, it’s a little more complicated to substitute them for wool or other animal fibers. Because they’re essentially made of plastic, wet blocking has minimal impact on the final project. If a project needs significant blocking to look right (think a lace shawl) it may not be possible to switch from a natural fiber to a man-made fiber.

Plant based fibers like cotton, linen, and hemp can be swapped amongst themselves without too much trouble. These fibers usually have a lot less loft and stretch than wool or wool substitutes. So, while the plant based yarns can often be swapped between each other without too many adjustments, they will require adjustments if they’re being used in place of wool or other animal fibers..

Man made fibers like rayon, bamboo, and Tencel (also known as semi-synthetics, and regenerated cellulosic fibers) are another tricky group. They usually require similar care as plant fibers, but often have different physical properties. Some are made to mimic plant fibers (usually cotton) and can easily be swapped with those. Often, they’re made to be smoother and with more drape, like silk. These can sometimes be swapped for silk, but won’t be direct analogs for plant based fibers.

Silk is another tricky fiber to substitute because how the silk is processed significantly impacts the yarns physical characteristics. Reeled silk (silk wound off the cocoon in one continuous piece then spun) is the shiniest and smoothest form. It isn’t often used in knitting yarns. Polyester fibers can give you a similar look, but they won’t have the same stretch or drape. Silk noil (aka peace silk or raw silk) can sometimes be swapped with a very soft cotton or a man made fiber with a similar texture. You may get a little less drape, but generally these will work well. Spun silk (silk fibers cut into shorter pieces before spinning) is very common as an ingredient in yarn blends and also used on its own. It can swapped with some man made fibers. Look for bamboo, Tencel, or other similar yarns labeled as “silky” and you may find a good equivalent.

Blended fiber yarns can also be swapped with or for single fiber yarns or other blended yarns. Pay most attention to how much of each fiber is included. Small amounts of different fibers are often added to yarns to change the look or improve the performance. Little bits of silk are often added to wool or linen to give them a nice shine. A bit of Nylon is often added to wool for strength. And wool is frequently blended with Acrylic to make more economical yarn. The higher the percentage of a fiber in the blend, the more it needs to be taken into account when you’re analyzing your yarn. For example, a 90% merino wool and 10% silk yarn could usually be swapped with a 100% merino wool yarn, a 90% wool and 10% cashmere yarn, or a 90% wool 10% bamboo yarn.

Yarn Size

Next, what size is the yarn? The listed yarn size will either be a number or a traditional name like “lace” or “worsted.” Australian and some UK yarns will be labeled according to ply, which doesn’t actually relate to the number of plys the yarn is made from anymore, but persists nevertheless. This can tell you a lot about the size of the yarn, but there is still room for variation within these categories.

To get a better idea of what I’m working with, I like to look at the ratio of yarn weight to yards of yarn. If I have two yarns that have similar weight to length ratios, that also happen to be made out of the same fiber, then usually they can substituted on a 1 to 1 basis with minimal changes.

But what do you do if you can’t find the right weight yarn in the size/color/fiber combo you want? You may consider holding your yarn double or triple. This isn’t an exact science, but the general rule is that you look at the yardage to weight ratio of the yarn your want to use and the yardage to weight ratio of the yarn in the pattern and try to make your total yarn match that. Susanna Winter of Talvi Knits has a great post explaining all the math behind yarn held double.

Yarn Construction

Two yarns can be exactly the same size/weight, but still function differently based on the number of plys and other construction variables. Generally, singles yarn (yarn spun with only one ply) is weaker than yarn spun with multiple plys. So, it might not substitute well in cases where strength is required.

Yarns made with 4 or more plys, usually appear smoother or more tube-like than 2-ply or 3-ply yarns. In most cases this won’t be a dealbreaker, but it may change the visual texture of your finished piece. If you’re working on something with a complex pattern, a yarn with really distinct plys may be a distraction.

Things can get a bit more complicated if you’re looking to substitute art yarn, slub yarn or novelty yarn. Any yarn that spun unevenly is going to behave differently than the more common consistently spun yarn. If you’re trying to switch to, from, or between specialty yarns be prepared go through several preliminary swatches and make adjustments on the fly.

Swapping Knitting Needle Sizes

I’ve written before about choosing knitting needles and my favorite needle types. When you’re thinking about changing needles, the most important thing to remember is that needles have two different relevant measurements: length and circumference. Changing the circumference of the needles will alter the size of the loops you make, which changes your gauge. Changing the length of the needles doesn’t impact the gauge, but may make the project more difficult to knit.

Needle Circumference

There are more than a few systems for numbering knitting needles, so it can get pretty confusing. Knitting needles that use the UK system get smaller as the numbers get bigger, while US knitting needles get larger as the number gets larger. Most needle packages and patterns also include the measurement of the needles in millimeters. See the chart below to compare.

If you knit a gauge swatch and find that your gauge is larger than intended, the solution is to switch to a pair of needles with a smaller circumference. And if you knit a gauge swatch that’s too small, switch to a larger set of needles.

The reason that variation in gauge happens, is that some knitters hold their yarn with more or less tension than the original pattern designer. Yarn has various degrees of stretchiness, so if you’re holding the yarn with more tension it will stretch more. When the loops relax as they come off the needle, they’ll be smaller than those made by a knitter with looser tension. I’m more likely to need to switch needles when working with smaller needles because there is less margin for error. Stretchier yarns are also more likely to need adjustment because tension differences are magnified.

There are other reasons you may want to change the size of your needles, however, these are best left to experienced knitters who are comfortable with the basics of pattern design. You can change the size of a garment by knitting using bigger or smaller needles (and thus a bigger or smaller gauge) than intended. However, this will change the drape of the fabric and there’s a chance that it could have other impacts as well. You can also change the gauge in order to get a looser (more drape) or tighter (stiffer) end fabric, but that also will change the sizing of the pattern and may have unintended consequences.

The one place where I might recommend switching up your knitting needle sizes to anyone is on ribbed bands, such as around the base of a hat. If you find that the ribbing of a pattern is too loose or stretches out too much during wear, go down a needle size for the ribbing, then switch back to the needles that knit at gauge for the rest of the project. This will tighten up the ribbing without effecting the rest of the project.

Needle Length

Knitting needles need to be long enough to fit all of the stitches of your project comfortably. Needles are too short for your project if the stitches are bunching up in a way that makes it difficult to knit them or, in the case of double pointed needles (DPNs), in danger of falling off the other end.

Straight needles and DPNs are too long if they feel awkward to use. Circular needles are too long if your project is being stretched out as you knit. To find the right length of needle to use, look at the schematic for your pattern.

In most cases, if you find part way through that you want longer or shorter needles, it’s easy to change them. You can either slip your stitches off your current needles and onto the new ones or knit a row off the old needles and onto the new.

As long as the needles are the same circumference theoretically, there should be no sign of the change. However, if the new needles cause you to change the amount of tension you’re putting on the yarn you might find a visible line develops in the first row after the change. This may block out, or it may not. To decrease the likelihood of a line, make sure your new needles are the same material as your old ones (swap bamboo for bamboo, metal for metal). You also may want to make the swap at a natural break in the pattern. Like when transitioning from ribbing to stockinet.

About the Pattern Used in this Case Study

The hat used in this case study is a simple beanie style hat that has a ribbed band at the bottom and a slouchy loose crown. It uses two different lace patterns (a border and a floral motif). I designed it to be an approachable first project for a confident beginner, because I needed a hand knitting project for the college level knitting class I teach. You can read more about the hat and get links to the pattern on my post about the Slouchy Lace Hat.

Experiment 1: Replacing Wool with Cotton

The original yarn I used for this project was Malabrigo Rios. This is a widely available four ply worsted weight yarn made of superwash merino wool. Since I assign this pattern as a required project, I wanted to make sure I could accommodate students who for ethical or physical reasons couldn’t use wool. I went with Blue Sky Fibers Organic Cotton Worsted yarn as my substitution because I was easily able to pick it up at my local yarn store it was available at two of my go-to online yarn sources: Jimmy Bean’s Wool and The Woolery.

An important thing to note right off the bat about the cotton yarn is that the yardage to weight ratio is much different than the wool yarn. Rios gets 210 yards to 100 grams, while the blue sky only gets 150 yards to the same 100 grams. I usually end up with a decent amount of the Rios left over after knitting one of these hats, so I didn’t think too much about it at the time, but that almost caused me problems

When I compared the two yarns side by side the differences were immediately noticeable. The wool yarn was significantly stretchier and much more compressible. The cotton yarn (while lovely) felt hard and stiff in comparison. There was nearly no stretch to the cotton yarn at all.

I started knitting a gauge swatch with the cotton yarn using the same size 8 needles I used for the wool version, but it was immediately clear that I was going to need to size down. Because it didn’t stretch at all when I wrapped it around my needles, the loops created during the knitting process ended up much larger than my wool sample. So, I frogged my work and ordered size 7 needles.

The size 7 needles, ended up being too big as well, so I frogged my gauge swatch again (at this point I realized I should have saved my swatches for this post, but such is life). The size 6 needles got me close enough to the correct gauge that I decided to move on to my main hat.

Knitting using the cotton yarn was a little harder on my hands than the wool yarn. However, as long as I kept my tension from getting too tight, it wasn’t a problem. I did however, get a bit nervous at the end because I nearly ran out of yarn! It was an intense game of yarn chicken, but in the end I had only about 2 yards of yarn left.

The finished hat felt a little heavier and denser than the wool version. This makes sense because the yarn it’s self was heavier and had less bounce to it. The ribbed band at the bottom had a smaller stretch range. At rest, it was about 22 inches wide and fully stretched it was limited to 30 inches. The orginal is about 20 inches at rest and can usually stretch to about 40″ fully extended. This doesn’t make a huge difference in sizing (30″ is more than enough for even the biggest head), but those with smaller heads may find it a bit too big.

Visual, I liked the cotton version. It was a little stiffer, but still draped well. The finished fabric had a bit more texture, but because I used a solid color this time, the pattern was just as visible. I might avoid using a really variegated color way of this yarn in this project (that might be too much), but I would definitely consider using textured yarn to knit lace again.

Experiment 2: Going Down a Needle Size

While I liked the overall fit of the original hat pattern, the band did feel a little loose on me. So, I decided to see what would happen if I knit the same pattern using the wool yarn, but at a smaller gauge. This time I chose the color Medusa (276).

I first knit a gauge swatch using my size 7 needles. While there was a clear difference in stitches per-inch (horizontally 5 vs 5.5, vertically 6 vs 6.5), the swatch didn’t feel significantly different than the original size 8 gauge swatch. Superwash wool tends to loosen up and grow a bit after wet finishing, so I didn’t think that there would be a big difference between the two needle sizes, but I decided to cary on anyway, you know, for science.

There was no difference in knitting experience between the two needle sizes. I was knitting at the same tension, so I didn’t feel like the loops were smaller. The fabric felt the same while in progress.

It was only after blocking that the size difference became clear. The size 7 needle hat was much smaller than the size 8 needle hat. When I tried it on, the size 7 needle hat did feel a bit more secure around my head, but the rest was a little awkward looking. It just didn’t drape as nicely, but because the superwash wool grew a bit, it also didn’t fit snuggly to my head.

Conclusion

A knitting project has many variables, but the yarn choice and needle size are two very impactful ones. Both the yarn and the needles can be changed, but whether or not this results in a successful project is dependent on your end goals and the specific changes you make. I hope this article has demystified the process of substituting yarn and changing needle size for you a bit, but I know that the only way to know for sure is to go out there and knit something!

Have you had any successful or disastrous swaps while knitting? Or do you have any tips that weren’t covered here? Leave a comment below or let me know over on Instagram!