Yarn Count Explained:
Understanding the labels on yarn packages
This is an excerpt from Peggy’s new book, the revised edition of Book #1: Winding a Warp and Using a Paddle, that just came out in July. This is information not in the first edition and comes in the extensive new chapter on Sett. 
Table of Base Counts of Threads

Yarn CountThere are official standards for measuring the number of yards in one pound of yarn. These standards were created by cloth manufacturers in the nineteenth century. The standards refer to the weight given to a given length of thread. For cotton, they used a reel with a circumference of 1 1/2 yards or 54″; for linen, one of 2 1/2 yards or 90″; for woolens, one of 2 yards or 72″. Silk uses the cotton reel. A 1 ply thread of cotton wound around its reel = 1 1/2 yards; 80 threads = one skein or 120 yards; and 7 skeins = one hank or 840 yards or one pound! So, now we know that there are 840 yards (one hank) of one ply cotton thread in one pound. This is the base measure or the “onecount.” Linen is calculated in leas, where 1 lea = 300 yards of one ply linen = 1 pound. Worsted is measured by counts. One count = 560 yards of single ply worsted = one pound. See the Table of Base Counts of Threads for some other base measures (onecounts). Now, it is obvious that a very thin yarn will take more yards to weigh a pound than a thick yarn would. On the package or cone of yarn is a fraction which tells you how your yarn relates to the base measure. It also tells you how many plies the yarn has. You need to know this because the measure of yards per pound is based on one ply thread. Say your package of cotton thread has a fraction of 3/2, for example. The top number tells you the size of your yarn and that it is three times the base measure or 3 x 840 = 2520 yards per pound. The bottom number is the number of plies, which here is 2 (2 ply). You know what one ply of your yarn is, so divide the total of the yards above the line by the number of plies. 
Simple! Unfortunately, some yarn makers put their fractions upsidedown. Usually, you can consider the smaller number to be the plies and the larger number to be the size. If after your calculations you get a number that makes no sense, try flipping the fraction and recalculating. If you have the yarn in your hands, you can count the plies, so you can tell which part of the fraction refers to it. 
Taken from: Book 1: “Winding a Warp and Using a Paddle”
Thanks, Peggy! This is the clearest explanation of yarn sizes I have seen yet. I will add it to my resource list for my students.
It is also in my book, Weaving for Beginners. It’s what I taught my beginning classes for 10 years or more. Peggy
thank you..a very experienced knitter on knitting paradise led me here when i asked a question of what does 14/2 mean on the inside of a giant cone of cotton rayon yarn..my figure comes out too 5880 whopping yards of yarn..i took 14 divided it by the ply=(7) and then took 840 x 7=5880..Im not a weaver,machine knitter or a spinner..Im a knitter of only a little over 2 yrs and I just could not say No when i bought this giant cone of cotton rayon for $19 bucks. since my yarn is not just cotton but has rayon also would you say my figures are close on yardage?
carolyne
If you have a pound of yarn, you do have that many yards! Good for you! My mentor explained that thinner yarns are cheaper than fatter ones because there are more yards per pound. Peggy
I used to use two, three, or 4 or more strands as one yarn when I got a big cone of thinner stuff than I wanted. Balling or spooling it takes time, of course. Peggy
Hi Peggy, thanks for your explanation. I’m still just learning about all this. 🙂 If I have some linen thread that is 30/3 and some other linen thread that is 30/2, will they be the same thickness? I do understand that the second number means the number of plies. Is the 30/3 made up of 3 thinner plies to make the same thickness as the 2 plies that make up the 30/2? OR do each have the same thickness of ply (as denoted by the 30) so therefore the 30/3 is 50% thicker than the 30/2? So I guess what I am asking is does the 30 refer to the individual ply or the thickness of the combined plies? Thanks so much!
The 30 refers to the size of the ply. Therefore 30/2 (2 plies) is smaller than 30/3 (3 plies). Yarn counts are described in my book, Weaving for Beginners. Grist refers to the size of yarns and is described in y book as well.
Thanks Peggy. Very much appreciated!
Hi Peggy,
Thanks for this explanation. It’s the most helpful one I’ve found online yet. I’m a beginning machine knitter and finding it very difficult to decipher the weight of the cones of yarn I’m trying to buy online without seeing the yarn itself. Is there an easy way to relate the fractions to the weight definitions that hand knitters are familiar with fingering, sport, DK, worsted, ect.? It seems that the numbers are all a jumble and I can’t spot a pattern to them to clue me in to the weight description.
I had a hard time with knitters’ numbers, too and gave up trying to make comparisons. Seems yarns per pound is easier for me but knitters are used to other ways.
I am am Australian and fairly new to weaving. So far, I have used patterns which indicated what yarn and what size reed to use. I use both a rigid heddle and a floor loom.
I would like to now weave without using a pattern. How do I decide what size reed to use? For example, if I use 8/2 cotton, can I use a twelve dent reed, or do I need to double up the cotton for a balanced pattern?
If I use what in Australia is known as worsted, do I use an eight dent reed?
Our yarns are also metric just to make life more difficult and in many cases, the UK system of measurement is used, ie Aran, worsted, etc.
So it’s putting the dimensions of the yarn with the size of the reed which is really confusing me.
For weavers, most everything is based on yards per pound. If you know that you can then decide on your ends per inch and from that the reed. (It’s highly desirable to have two ends per dent.) Other factors can come into the calculation of the sett (epi) eg. weave structure, slippery threads, etc. etc. I think it would be a good idea for you to get my book, Weaving for Beginners”. I have a lot of information on this subject as well as getting started and a series of weaving things to try as you progress. I made this book for you. Since the shipping to Australia is so expensive, I’ll enclose my book #1: Winding a Warp & Using a Paddle” as a gift. In it is a whole chapter on the subject (sett). I hope I’ll hear from you since you are getting started. Anyhow, you work with yards per pound. Hope this helps. Peggy PS You can order on my website–be sure to remind me to include the extra book. You can always email me with the reminder as well: peggy@peggyosterkamp.com.
Thank you for posting this tip. I have been weaving for many, many years and never fully understood how the numbers came into being. I understood the number for plys and that the smaller the number on top, the fatter the yarn (and thus, less yards per pound) but I didn’t know the background for how that number is determined. This information comes at a perfect time for me. We’re doing a series of STEAM based learning programs in my library and I was thrilled to have the opportunity to introduce our teen patrons to weaving, while also showing them that there is a practical reason to pay attention in math class. I will be adding your information to my program. Thanks!
This would be a great application of a math problem–so convoluted but a reason for it. Peggy
Hi Peggy, Thank You so much for sharing your tips! Can you tell me the difference between “wool cut” and “wool run” in the chart above, and when to apply them? I was given a tub of wool cones and need to know which figure to use.
Thank you in advance!
plz say simple words for diffination of count
If you need more information, let me know what I should explain better. This is copied from my book, Weaving for Beginners. Peggy
Yarn count is a system of describing the size of yarns.
Usually, the number of plies is given as well. Together,
they denote the size of the yarn by indicating the
number
of yards per pound. (The more yards per pound,
the finer the yarn is.) Typically, there are two numbers
given in the form of a fraction. The size or count is given
in the upper part of the fraction and (mostly) the ply
portion
is on the bottom. The ply portion of the fraction
is explained below.
To explain how confusing the system is for identifying
the size or the count, I will explain how the count
(size) for cotton was determined in the nineteenth
century. Each fiber has its own way of determining its
count, however.
For cotton, number one is the size of one thread made
from one pound of cotton with a length of 840 yards.
This length came from measuring a cotton thread on
a reel 1 ½ yards (54″) in circumference. 80 threads
wound around the reel made up a skein of 120 yards,
and 7 skeins made up one hank, or 840 yards, and that
amount of yarn weighed one pound. The “base count”
for number one cotton (one strand) is 840 yards per
pound. Other fibers used different size reels and arrived
at different base amounts, and some are shown on the
next page. (All fibers are considered to be number one
at their base counts, like number one worsted for wool,
number one lea for linen, etc.)
From number 1, other counts are derived. The count of
2 is the size of a thread if twice this yardage (2 x 840 or
1680 yards) weighed one pound. Number 3 would be
three times the number of yards in one pound or 840 x 3
= 2,520 yards. It is obvious that a very thin yarn will take
more yards to weigh a pound than a thick yarn would.
Therefore, a higher number would indicate a thinner
yarn. Labels tell you how your yarn relates to the base
number (no. 1) for that fiber (here, the example being
cotton). Next, the bottom number of the fraction or the
number of plies in the yarn must be taken into account.
For example, 5/2 on a label for cotton yarn tells you
that the size of the thread is no. 5 and that the yarn
is composed of two plies. A plied yarn is a yarn that is
made up of more than one strand. For example if you
folded a oneply yarn on itself, you would get a 2ply
yarn that would still weigh the same amount—in these
examples, one pound—and would be half as long
For the example of 5/2 cotton, we can calculate that
the “5” signifies a thread that is 5 x 840 (4,200) yards
long in one pound. The number 2 below the line in the
fraction signifies the number of plies. So, if there are
two plies in this one pound instead of one, there must
be half the yardage in the pound (2100). And that is
the way the yardage is calculated. You know what one
ply of your yarn is (the count), so divide the total of the
yards by the number of plies.
Figure 497 shows what a plied yarn looks
like where diagonal lines can clearly be
seen on the yarn. If you look closely at the
cut end in the illustration, you can see that
there are 3 plies in the yarn, or 3 strands.
Unfortunately, some yarn makers put their
fractions upsidedown. Usually, you can
consider the smaller number to be the
plies and the larger number to be the
count or size. If after your calculations,
you get a number that makes no sense, try
flipping the fraction and recalculating. If
you have the yarn in your hands, you can
count the plies, so you can tell which part
of the fraction refers to it.
Summary: The fraction given for a yarn tells if it is
a thicker or thinner yarn by indicating the number of
yards per pound. If cotton has a base count of 840 ypp
for one strand, you can see that by looking at the counts
only, 10/2 cotton (ten times the base count or 10 x 840,
or 8400) has more yards per pound and, therefore, is
finer than 5/2 cotton (5 x 840 or 4200). Finally, by
dividing the count’s yyp by the number of plies you
get the yards per pound for 10/2 cotton as 4,200 ypp.
The 5/2 cotton has only 2,100 yards in a pound
(5 x 840 = 4,200 divided by 2 = 2,100 ypp).
Otherwise, look at the label for the yards per pound.
Thinner yarns have more yards per pound than thicker
ones. Look at the Yarn Size Chart on page 264.
In your weaving life, you’ll become familiar with some
types of yarns and will remember some fractions and
what they mean. See the Base Counts chart on the
previous page.
For more information, see my first book, Winding a
Warp & Using a Paddle on pages 91 and 113116.
What is the length of one pound of size 1 alpaca?
Hello Peggy,
What about markings where the smaller number is higher, such as 12/6,12/9, 12/18, 20/6 as in seine twine? How do these compare to the ply based system?
Thanks
Is there an in depth resource that explains yarns other than those manufactured in North America? This is really helpful, it I find that sometimes I am looking for a very fine yarn that is likely only produced elsewhere. Thank you!
Yes. In my book Winding a Warp & Using a Paddle I discuss Deniers, Worsted count(WC); Metric Count (m.c. or Nm.); and the Tex system, tooell. there are conversions from one to another, as well. I think I covered all the bases.
Peggy