What does "yarn weight" mean?

(Photo from Downton Abbey, Season 1 / Episode 2)

One of the most frequent requests we get for assistance in our shop is to help people find the right yarn for their project. Either the pattern calls for a very specific yarn and doesn’t give information on equivalents, or the pattern calls for a specific “weight”of yarn but assumes the crafter knows exactly what to ask for. If you’ve ever seen a pattern that calls for “fingering-weight yarn,” or “baby yarn,” or “a #2 yarn”, you’ve dealt with yarn weight.

This is a vast and complex topic, but let’s break it down into some basic bullet points this week.

1 - “Yarn weight” is kind of* another way of saying “yarn size.”  (*it’s complicated)

When you search for yarn in a certain weight, you’re looking for a yarn that, due to its general ratio of yards to ounces (or meters to grams), is likely to act the way you expect it to in a given pattern. This is a bit of an overgeneralization, as the way a yarn is spun can cause it to behave like other yarns in a given “weight class” but look like a very different yarn weight on the shelf. 


2 - There are at least 3 ways that people assign a weight to yarns.

You’ll see yarn weight assigned solely based on the ratio of yards to ounces / meters to grams, or by stitches per inch, or by wraps per inch. The first two methods are the most common; wraps per inch (or WPI) tend to be more used by weavers and spinners. 


3 - Not everyone agrees on the “correct” way to assign a yarn weight classification.

The more information you have on a given yarn, the more of an understanding you have on how that yarn is likely to behave in a given pattern, or on a given hook or needle size. Most of our commercial yarns at the shop have the ratio on their labels as well as the stitches per inch measurement.

In the shop, I tend to rely pretty heavily on the ratio method to assign yarns their spot in the shop since the shop is laid out in yarn-weight order; however, I also take into account technical knowledge about how some of our yarn options are spun when I’m making that decision. (More about that in a later post!) When I’m working with customers to decide on which yarn is right for their pattern, the ratio method gives me a ballpark idea of where to look for a good match; the washed, blocked swatch will give us the final answer with the most accuracy.

There’s a group called the Craft Yarn Council that has a chart with all kinds of information on how yarns in the same “weight class” can be measured - you can get it for free at craftyarncouncil.com.


4 - Crocheters and knitters often use different scales to describe the same yarns.

Crocheters in the US tend to use a numerical scale that runs from 0-7 to classify yarns. Knitters in the US tend to use a word-based scale (cobweb, lace, fingering, sport/baby, DK, worsted, aran, bulky, super-bulky, jumbo) to classify yarns. They can be used interchangeably to describe the exact same yarns, just in different terms. 


5 - Even if a yarn is labeled the same weight as what you need for a pattern, not all yarns in the same yarn weight are equal!

Yarn weight categories cover a LOT of ground. Just because something is classified as a “worsted-weight” or #4 yarn doesn’t mean it will knit up exactly like the #4 / worsted-weight yarn that the designer used - especially if the designer didn’t specify which yarn they used! A yarn that has alpaca content and 175 yards per 100 grams isn’t generally going to behave the same way as a mostly acrylic yarn that has 230 yards per 100 grams, even if they’re both called worsted-weight yarns by the yarn company or the yarn shop.
This is where gauge swatches come into play. Pattern yarn recommendations are ultimately guidelines. Even if you use exactly the same yarn and hook/needle size as the designer, you might not be able to get the same gauge they published in the pattern because you crochet/knit more loosely or tightly than they do. 

So there you go - watch this space over the next few weeks for more posts about specific aspects of yarn weight. We'll post a new article each Tuesday and let you know on our social media feeds (Instagram, Facebook, and Threads).