Not all yarn is created equal. When comparing yarn, some can be thicker and some can be thinner. Below is a picture of three different yarn weights. You can see how the thickness varies between each of them.

So how do you know what yarn is right for your project? Most patterns will have a materials or supplies list in the beginning of the pattern. It may recommend a certain brand of yarn they used, and/or give you a term like “bulky” or “#5 weight”. But how do you know what weight a yarn is? That information can be found on the yarn label. So why don’t we look at some yarn labels?

First, is a picture of the label that is on the dark grey color yarn pictured above. Do you see the symbol that looks like a skein of yarn with a “5” on it and the word “BULKY” over top? This symbol refers to the weight of the yarn. So this particular yarn is categorized as a bulky weight or a #5 weight. Now why don’t we compare the labels from the green and yellow yarns pictured above as well.

Here is the label from the green yarn. The symbol is similar, but instead has a “4” in the center of it and the word “MEDIUM” over top. So this yarn is categorized as a medium weight or a #4 weight.

Lastly we have the label from the yellow yarn. The symbol still looks similar, but has a “1” in the center and the words “SUPER FINE” over top. So this yarn is a super fine weight or a #1 weight. So that seems pretty simple to figure out what weight a yarn is by reading the label, right?

But now imagine the pattern you are wanting to work on calls for a worsted weight yarn or sport weight yarn. Different yarn weights can go by many names. It can be confusing. So I made a chart to help with this.

I made a separate chart for lace weight or #0 weight yarn. This weight is a bit frustrating to me because it varies in thickness quite a bit, but it is all considered a #0 weight. So I tried to break it down.

You may have noticed the chart has “Wraps Per Inch” in it. This is another way to measure yarn thickness. It is exactly as it sounds. You wrap the yarn around your crochet hook, pencil, or whatever you have handy. Just make sure it is uniform in thickness, until the wraps reach an inch, and then you count how many wraps. You want to make sure your wraps aren’t overlapping or too tight. But also you do not want gaps between the wraps either. So you can see here that it took 9 wraps to reach an inch. So this would be 9 WPI.

Measuring wraps per inch is also helpful if you lost the label on your yarn and are unsure which weight it is.

Now that you understand the different yarn weights, does it matter what yarn weight you use in a project? When I first started making crochet items I didn’t think it mattered so much. I would pick out whatever color yarn I liked and would start my project. And that is why some of my early projects turned out too big or too small, and just didn’t look very good. To help you understand why this happened, let’s see what a crochet swatch of those three different weight yarns look like. I did the same number of stitches, the same number of rows, and used the same hook for each one.

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The #5 weight yarn came out to a 4 inch by 4 inch square.

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The #4 weight yarn came out to be a 3.75 inch by 3.75 inch square.

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The #1 weight yarn came out to be a 3 inch by 3 inch square.

So now imagine the project you want to make a beanie style hat. The pattern calls for a #5 weight yarn. You go to the craft store and pick out a #1 weight. Now the pattern says the hat should end up being 20 inches around and 8 inches in height. You make the hat using the #1 weight yarn, but once it’s done it only measures 15 inches around and 6 inches in height. What happened?

When you compare these swatches, the #1 weight works up 1 inch smaller than the #5 weight. So using the #1 weight instead of the #5 weight you would lose 1 inch for every 4 inches of your project. So over 20 inches, that adds up to a 5 inch difference. And over 8 inches, it a 2 inches in difference. Now imagine it was a blanket you were making. And it was suppose to be 60 inches long by 40 inches wide with the #5 weight yarn. It would be 15 inches shorter in length and 10 inches shorter in width using the #1 weight yarn. So you can see how understanding and using the correct yarn weight can make a huge difference in your completed project.

Is this to say you can never substitute yarn weights? Absolutely not, I do it all the time. But I am particular on which projects I decide to do this with though. Let’s go back and look at the #4 weight yarn swatch, when compared to the #5 weight yarn swatch, it is only a quarter of an inch difference. So now let’s say you were to make that same hat using the #4 weight yarn instead of the #5 weight yarn. It would come out 1.25 inches smaller around, so instead of 20 inches it would be 18.75 inches. And it would be half an inch shorter in height, so instead of 8 inches, it would be 7.5 inches While that is still smaller than the pattern intended, if you have a smaller head it might work for you. And if you were to make the blanket that was suppose to be 60 inches, using the #4 weight yarn instead of the #5 weight yarn, it would end up being 56.25 inches in length and 47.5 inches in width. This may be a small difference to you, and you do not mind the blanket a little smaller. So there are times substituting different weights of yarn in a project can work. The times I usually stick with the correct yarn weight is with clothing. It is the only way to ensure it fits properly.