Yarn 101

The means of measuring yarn size seems to be a common source of confusion among knitters. Interestingly enough, it’s one of the first things that must be mastered by weavers in order to get a warp on the loom.

About Yarn

I’m not going to bother repeating a lot of yarn facts because I believe they’ve been explained well enough by The Craft Yarn Council of America and Fabric University. If you really want to understand your stash better, you’ll want to bookmark these sites. As you read the rest of this article, you may need to refer to these sites for terms you’re unfamiliar with.

Yarn Phobia

If you have a reasonably large yarn stash, chances are pretty good that you’ll find all sorts of labels with different information on each skein, ball or cone. Worse still, you’ll find a few items in your stash that don’t have labels at all. And worst of all, you pass up the opportunity to buy another yummy cone just because you don’t know what it is. So how are you supposed to compare yarns if different manufacturers don’t use the same measurement system?

The fact is that while the systems may appear to be very different on the surface, they all accomplish the same thing and that is to identify yarn in terms of size and weight. Now before you go getting all excited, it’s not quite that simple… but hopefully what seems to be a sea of inconsistencies will make a lot more sense by the time you’ve finished reading this article.

Yarn Weight

In recent years, some manufacturers have begun using standard symbols to categorize yarns in terms of its size. While this practice is becoming more common, it isn’t what I would call widespread and you’re likely to come across many labels that don’t use the symbols.

SymbolDescription & ExamplesStitch Gauge
For Stockinette
Measured Over 4″
Super-fine: sock, fingering, baby27-32
Fine: sport, baby23-26
Light: DK, light worsted21-24
Medium: worsted, afghan, aran16-20
Bulky: chunky, craft, rug12-15
Super-bulky: bulky, roving6-11

Yarn Count

Yarn count, sometimes referred to as thread count, is the number of yards required to make one pound of size 1 cotton, linen or wool:

840Cotton, spun silk, rayon and acetate
300Wool (cut system)
560Worsted wool, acrylic (spun system)
1600Wool (run system)
300Linen, hemp, jute and ramie

Contrary to what one might think, size 1 (or #1) is the largest possible size for a single strand of any fiber. A pound of #2 yarn contains twice the yardage of #1, but is half the diameter; #3 contains three times the yardage and is one-third the diameter.Two strands of #2 yarn will have approximately the same diameter as one strand of of size 1 yarn.Plying two strands from a 1 pound cone of #2 yarn will yield approximately the same yardage as one pound cone of #1 yarn.

It should be apparent at this point there are three factors that affect yards per pound (YPP):

  • the type of fiber
  • the number of plies
  • the size of a single ply

Since the count system is mathematically accurate, it provides the foundation for identifying unlabelled yarn and calculating yarn factors that aren’t listed on the label.

Given three of the four factors (count, size, plies and yards per pound), you can easily calculate the missing information:

YPP = size ÷ plies x count

count = YPP ÷ size x plies

size = YPP ÷ count x plies

plies = count ÷ YPP x sizeYarn that is measured by the count system will have a label that reads something like:

10/3 cotton

This label identifies the yarn as a 3-ply #10 cotton at 2800 YPP.

A Brief Chat About Wool

When you read the chart above, you probably wondered about the three different systems used in the production of wool yarn. You’ll find some interesting information about yarn numbers at sizes.com, but I’ll give you a brief summary here:

  • The most common wool systems used in the US are the cut system and the run system with the run system being the most common in all areas except Philadelphia.
  • In the cut system, coarse yarns are 5 to 7 cut, medium yarns are 18 to 21 cut and fine yarns are 30 to 35 cut.
  • In the run system, coarse yarns are 1 to 3 runs, medium yarns are 3 1/2 to 5 runs and fine yarns are 6 to 8 runs.

Wraps Per Inch (WPI)

WPI is a technique commonly used by weavers to determine the required sett (spacing) for warping a loom. This technique is often overlooked as a means of determining whether one yarn can be substituted for another, especially in cases where one of the yarns is a blend or when the two yarns have a different fiber content.

Because it’s easier to visualize the apparent size of a yarn from its WPI rather than its count or YPP, knowing how to determine WPI is an excellent tool for selecting new yarns or sorting your yarn stash.

I prefer determining WPI using a little tool I bought that is specifically designed for the purpose, but you can accomplish the same thing using a round pencil, broomstick handle or 6-inch piece of wooden dowel. Avoid wrapping your yarn around a flat ruler or stick — the sharp edge may affect the wrap and result in an inaccurate WPI.

  • Hold the pencil in one hand and use the thumb of the same hand to hold one end of the yarn against the pencil.
  • Use the other hand to wind the yarn around the pencil making sure each “wrap” is laying next to the wrap before it without stretching the yarn. The yarn should wrap naturally around the pencil and should be no looser or no tighter than its unwrapped state.
  • Once you have the pencil wrapped for at least 1 1/2″, use a ruler to measure off a 1″ section and count the number of wraps in 1″.
Lace18 or more
Super-bulky8 or less

Useful Tools

Electronic Kitchen Scale

My favorite is manufactured by Salter — it weighs up to 10 pounds to the nearest 1/8 ounce or 1 gram. It also has an auto-shutoff so I don’t drain the batteries when I forget to turn it off. Besides helping you identify your yarn, it comes in extremely handy for trading. If I want to give a friend 100 grams from a 2 pound cone, I turn on the scale, place the cone on the scale to get the current weight and start winding off onto a ball winder until it weighs 100 grams less.

WPI Tool

You can make one of these using a 5″ length of 1/2″ dowel:

  • Cut a narrow slit across one end.
  • Drive a small brad about 1″ away from the slit to mark where you’re going to start your wrap.
  • Make a permanent mark on the dowel exactly 1″ away from the edge of the brad.

Thread the end of the yarn through the slit to secure it, turn the corner around the brad and start wrapping. Stop wrapping when the yarn is at the 1″ mark. If you want a higher degree of accuracy, wrap 2-3 inches and divide the number of wraps by the length of the wrap.

You can also buy WPI tools from Nancy’s Knit Knacks. It comes with a laminated card that lists the WPI for the six standard yarn weights. The tool and card are small enough to keep in a side pocket of your purse so you always have it with you when you’re out and about.

McMorran Yarn Balance

A McMorran Yarn Balance can be used to quickly determine YPP with a pretty high degree of accuracy. You position the balance at the edge of a table and hang a small length of yarn over the arm of the balance. You snip tiny bits of yarn off the dangling ends until the arm is perfectly horizontal. Measure the piece of yarn that remains and multiply by 100 to determine YPP.

Name That Yarn

So now that you understand all the ins and outs of yarn count, weight and WPI, it’s time to talk about how you can identify that unlabelled cone in your stash.

I find that the simplest way to identify a yarn is to start with YPP. If you don’t have this information, you can use the McMorran balance mentioned above; or you can guestimate by measuring off a substantial amount of yarn (10-15 yards), weighing it and dividing the weight by the number of yards. Keep in mind that stretchy yarns need to be measured carefully in order to not skew the results. It may be useful to hang a yard stick on a wall and measure the yarn by letting it hang naturally.

Since yarn count is tied to the type of fiber, identification will be difficult if you don’t know what kind of fiber you’re dealing with. Fabric University has a great article on using the Burn Test to determine content. Keep in mind that the burn test may yield odd or inaccurate results if the yarn is a blend.

If you can figure out YPP and content, you’re home free. Simply count the plies and use the tables and formulas described in this article to figure out everything else.

I recently discovered a cone of very fine yarn in my stash. I was pretty sure it was wool, but I did the burn test just to make sure. I then used my McMorran Yarn Balance to determine my yarn is 8200 YPP. I untwisted the end and learned that my yarn was a 2-ply. I assume my wool is either cut system or run system because I know it was manufactured in the US, so I also assume the count has to be 300 or 1600; I’m going to start with the run system because I’m pretty sure this yarn was manufactured by Dorr Woolen Mills in New Hampshire.

Going back to my formulas, I first calculate the yarn size since that’s a definite unknown:

8200 ÷ 1600 x 2 = 10.25… since #11 would be an odd size, I decide my yarn is most likely #10. Now I’m going to use the other three formulas to check my work:

YPP = size ÷ plies x count10 ÷ 2 x 1600 = 8000
count = YPP ÷ size x plies8200 ÷ 10 x 2 = 1640
plies = count ÷ YPP x size1600 ÷ 8200 x 10 = 1.95

In the table below, you can see how close the numbers are between the formulas and the numbers I derived from my research. Since a difference of 2-3% is well within the margin of error, I decide my YPP is really closer to 8000 instead of 8200.