How to choose the best substitute yarn for your crochet project?
Sometimes you just can’t or simply don’t want to use the yarn recommended in the pattern for a certain project. Maybe it is not available to you, maybe it is too expensive, maybe you are allergic to a fiber or you simply want to use some of the yarn from your enormous stash. But you still want to follow through the pattern and get the same item. How to find than the best substitute yarn?

The basic things to consider when using a yarn substitution are yarn weight and content.
substitute YARN WEIGHT
No, you won’t be checking if the skein weights 50g or 100g, or maybe 200g and comparing it, (together with the length of yarn in a skein) with the yarn used in the pattern. As tempting as this can be, thinking that if two yarns have the same weight and length in one skein, it means they are good match will most often mislead you! It can be true sometimes, but that is not something you want to rely on.
You want to make sure that the yarn you are about to choose is within the same weight category as the original one. Then, look for the similar fiber type, whether it is acrylic, wool, cotton, some blends, if you want to stick to the recommended one. Or look for the fiber you’d want for the project. After you narrow down your options, look for the available colors and chose the best match for your crochet.
Let’s see how it works using my Rose Shells Crochet Scarf pattern as an example. I designed that pattern using Alize Burkum Classic 100% Acrylic yarn. I made a second sample with Alize Lanagold Classic made of Acrylic (51%), Wool (49%). The fiber composition was different, but the yarn weight and gauge were exactly the same. Let’s have a look!
This is from the actual pattern. I gave the information about both yarn I used, and I offered some ideas for possible substitutes. Alize Yarn is not as popular as all these other brands, but it is a great option for me since the yarn is excellent, and most of the popular brands are not available in my country. Even if I can order those, the shipping costs are, well, amazing (even though I live in Europe). So I decided that it would be a good idea to suggest some more popular yarns within the pattern itself and make it easier to crocheters who do not want, or do not know how to look for the alternative.

Main attribute to compare was, of course – yarn weight. There are different opinions about category 4, if Medium and Aran are exactly the same, but it seems like the difference is not as much in thickness itself, as in the feel of it (Aran yarn feels heavier). Anyway, I looked for the similar weight yarns.
Then, I needed to choose the fiber. For a shawl, anything from acrylic to wool is a good choice. You have a variety of options there. And the next thing to take into account here is the feeling. This is a shawl and you’d probably want it to feel soft and cozy.
Let’s try togeteher!
Let’s say your favorite brand is Red Heart and you want to make this scarf using some of their yarn (and this is no affiliate, just an example). You’d go to… let’s say Yarnspiration site (or any other yarn site) and choose Red Heart Brand.
REFINE BY BRAND: RED HEART
Next, you want to filter your search with yarn weight, and check the box
REFINE BY WEIGHT: #4 WORSTED (MEDIUM).
You will have a lot of possible options, so you’d want to narrow it down further with certain fiber type. Let’s choose an acrylic yarn for the sake of this example and check the box.
REFINE BY FIBER: ACRYLIC

We still have a lot of options here. Let’s say we’d like to make a yellow scarf to brighten up our cold, gloomy days and we check yellow color box.
REFINE BY COLOR: YELLOW

We are down to 9 options. We could now chose based on a price, or we can select one of the types (baby, classic or fashion). Let’s say we want it to be fashion yarn.
REFINE BY YARN TYPE: FASHION

And we are down to one – Red Heart with Love Yarn.
I would like to mention something else here. We know that all yarns within the same category are not the same. And since WPI is not the information we have here, we can look at the information about the gauge and hook size. Gauge is shown in sc stitches, so it doesn’t really apply directly to most of the projects. But we can use it as a guidance.
We want to make a shawl and the pattern asks for Medium Aran yarn, meaning we should choose the thickest option within the category if possible. Comparing the gauge here, we can see that 12 sc stitches (as a lowest number of sts per 10cm /4 in in this category) is showing us that that would be the thickest yarn and possibly the best option here.

This could be slightly confusing and I wouldn’t really bother too much with this unless the size of the project is essential. Even then, adjusting the hook size should do the trick!
In this case, we can see that our chosen yarn has a gauge of 14 sc sts and with 6.5 mm hook. In the case that the size was essential here, we might have wanted to consider a different yarn (with the gauge of 12 sc and maybe the same hook as in the pattern).
Anyway, by adjusting the hook size, most likely you can meet the gauge with any yarn in the appropriate category.
If you still find it difficult, or you simply don’t want to get into all these categories, there is this good site YarnSub you can use for reference. You can find a lot of possible substitutes here based on texture, yarn weight and density, fiber content, fiber qualities (e.g. drape, softness), or gauge (bear in mind here that this is a knitting gauge here!).