How can I determine a yarn's weight?

Question

I have a bag full of yarn from miscellaneous projects. In error, I never kept the labels for the yarn because "Why would I need to keep those?". If I am going to work on a project and need a yarn of a specific worsted weight, for example, how can I match the requirement to one of my balls or skeins of yarn?

After reading a small Wiki article about yarn characteristics I realize this might be hard to do and might just be a matter of guessing.

Some of the names for the various weights of yarn from finest to thickest are called lace, fingering, sport, double-knit (or DK), worsted, aran (or heavy worsted), bulky, and super-bulky. This naming convention is more descriptive than precise; fibre artists disagree about where on the continuum each lies, and the precise relationships between the sizes.

Answer 1

There are apparently several different methods for finding about what weight you're dealing with. All of these can have their own downsides but they're worth considering.

Note that, realistically, if you can't tell whether something is "sport" or "DK" but you know it's one of the two, it's probably not going to throw you off too badly.

Also note that the US and the UK have different terms for the same weights of yarn but that since stores sell yarn from around the world, you're likely to run into all of them regardless of where you live.

Wrapping

Wrapping is a method of testing the weight by seeing how many widths of yarn fit in an inch of space. It looks a bit like this:

You can wrap around the ruler itself or around something else like a pencil. The fewer widths of yarn that fit in an inch, the heavier the yarn is. Note that for thicker yarns, you might want to wrap more than an inch and divide to get a better count.

The downside of this is that not everyone wraps the same and yarn is squishy. They yarn in the image is very neatly wrapped but you could easily squash it together and get another 3-4 wraps in that inch.

Ply or strands

Generally heavier-weight yarns have more strands. This can be finicky with smaller weight yarns and it won't always give you the information you need because there's no real standard but if your yarn only has 2-3 strands, it's probably really light weight and if it's worsted it's probably 10 or 12 ply. So, if you use this in combination with wrapping (or some common sense) it will probably help you. There's a list of the ply to weight name chart on Ravelry.

By Gauge

You can determine whether an unknown ball of yarn will work for your project by making a gauge swatch. This requires that you are pretty comfortable with your stitching and are consistent but it should help. Use the recommended sized hook or needle for the project and follow the instructions for determining gauge for the project (if it includes those instructions) or use a base guide like the one here. If the stitch count per four inch swatch is really off, then it won't work. If it's good and it looks the way you expect, then go for it.

In this case, you should adjust for your own stitch style. If you know that you normally need to crochet with a 5.5 mm hook when the recommended size is 6.5, then crochet the sample with the 5.5 mm hook rather than the recommended one.

By Weight

Some people have really good scales. If you measure how long your yarn is and then weigh it (in grams) you should be able to find out the weight... because everyone wants to spend hours measuring the length of their yarn. The better your scale is (and heavier the weight), the shorter the length of yarn you can weigh.

I'd recommend that you weigh at least 10-20 grams worth of yarn and then figure out the length. Note that you don't have to cut the yarn to do this, just let the remainder hang off the scale and mark the measurement stop point with a small slip knot. It shouldn't affect the measurement too much.

Now that you have your weight to length measurement, you should be able to compare it to other known yarns and get an idea of what the "weight" group is. Though, note that the material your yarn is made of can affect its density so if you don't know what it's made of (which is likely since you don't have the label any more), you might want to try to figure that out, too.

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As an aside, labels are annoying to hold on to plus the cat probably ran off with them or ate them... but I recommend that you avoid getting into this situation by logging your yarn purchases somewhere. Either keep track of your receipts (if they give identifying info about the yarn) or, even better, track your purchases on a site like Ravelry. This is great because it often has everything uploaded already, so you don't have to manually enter any of the data except (if you want) color name and dye lot. The section you're looking for is called "stash" under "my notebook".

Answer 2

Not only yarn thickness but wraps per inch, whether the yarn has been spun woolen or worsted style (nothing to do with the weight), and the type(s) of fiber matter for matching. In plainer words, it seems fairly obvious: if two yarns have the same labeled weight ("DK," let's say) but one is 100% wool, worsted spun, and the other is 50/50 wool/tencel, they will look and feel different, with different densities.

Wraps per inch are more accurate than "sport" versus "DK" and so on.

Answer 3

@Matt: You are onto a question which seems quite straightforward at first, yet can sometimes be a bit more complex.

As @Catija reviewed above, there are many good ways to get a general idea of what your yarn weight is. These methods, along with experience, will usually get you quickly to that 'good-enough' answer about yarn weight and thus yarn yardage, so that your project can proceed as smoothly as possible.

However, problems can arise sometimes when you are figuring out yardage for similar-appearing yarns with very different densities. In the example previously mentioned, worsted spun and woolen spun yarns of similar circumferences can appear to weigh about the same - and yet they can actually have quite different weights - woolen spun being fluffy, and worsted spun dense. Here is a nice discussion on this difference, ala The Natural Fibre Co.

So, if while figuring out available yardage for a mystery yarn, you need a more exact yarn weight answer, there is one other option: a "Yarn Balance". This brilliant little tool can very accurately tell you the number of yards per pound of yarn, using a sample of the yarn several inches long. The link above has an excellent photo tutorial. (Photo from The Woolery:)

References:

The Natural Fibre Co.

The Woolery

Answer 4

Probably the most reliable method is creating a gauge swatch. Other methods such as wrapping or weighing may give you insight into whether your yarn matches the pattern, but it tells you nothing about how the yarn will perform when you attempt to use it to make the pattern. Every yarn crafter has differences in their yarn tension, which can make the same yarn appear bulkier or thinner in the finished piece.

The best practice is to eyeball your intended yarn (it should be obvious that a super bulky yarn won't work for a lace doily) and then follow the instructions in the pattern to make a swatch.

You can also create a small swatch in a standard size whenever you buy a new yarn, and safety pin the swatch to the ball or skein. Except for patterns that use special stitches, this mini swatch should work universally to judge the gauge, and it's less likely to get lost than the paper wrapper.