Understanding Yarn Sizes
Have you ever wondered what the different weaving yarn size numbers mean? Itís actually a pretty smart system and once you understand it, choosing the right yarn for a particular project is much easier! There are two numbers: one for the size of a single strand and the other for the number of plys (or strands twisted together).
The size (called the yarnís count) is determined by how many yards have been spun out of a pound of fiber. The thickest single-spun strand of each fiber is given a size of 1, with all other sizes being a multiple of that. For example, an 8/2 cotton yarn is 2 strands of size-8 cotton singles plied together. The larger the yarnís count, the finer the yarn has been spun. Imagine a pound of fiber that has been spun twice as fine as a size 1 strand of yarn: it will be half the thickness and twice as long.
So far so good! Now for the complications...
Every fiber weighs differently, so the count numbers donít correlate between different types of yarn (darn!). That means an 8/2 wool is a VERY different size than an 8/2 cotton. Following is a chart for the (a) standard number of yards per pound in a size-1 strand:
Cotton, Rayon: 840
Linen, Hemp: 300
Woolen spun wool: 256
Worsted spun wool: 560
You can use this chart and the yarnís count to determine the number of yards per pound of any particular yarn. You simply multiply this Ďmagic numberí by the yarnís actual count number to get the number of yards per pound. For example, a pound of size-1 cotton would give you 840 yards of yarn (840 x 1); and a pound of 8/1 cotton would be 6,720 yards of yarn (840 x 8). What about plys, you ask? Easy! Simply multiply by the count, then divide by the number of plys. That means one pound of 8/2 cotton would have half as many yards as a pound of 8/1 cotton.
The same process works for all other fibers, you just have to substitute the correct number for the type of fiber that the yarn is made of. Which brings up the next complication... Fiber mixes. What if you have a yarn that is part cotton and part linen? (or any other mix) Unfortunately, the correct number to use will differ by manufacturer. Some will use the count number for one of the fibers in the mix, others will use a new count number that falls somewhere between the two fibers. It is helpful to ask (or look at the yarn in person) if you are unsure of the actual size of a mixed yarn. The Swedish cottolin (cotton-linen blend) that we carry from Bockens is labeled 22/2, but it is actually very close in size to an 8/2 cotton and can be substituted for it in any draft.
Next complication! Some countries will swap the count and the ply order, or just swap it for some types of fiber (in the US we tend to swap the order on wool yarns). In Canada, an 8/2 cotton would be called 2/8 instead. Pay attention to the context and the correct meaning is usually clear (an 8-ply, size-2 yarn would be rope, and not good for dishtowels).
Finally, it helps to remember that the count method is determined by the number of yards in a pound rather than the actual thickness of a yarn. Looking at sett charts for deciding your ends per inch is a great place to start but the actual thickness of a yarn differs by manufacturer and you might want to adjust your sett accordingly. This is most apparent in wool yarns where it is possible to get a very light and lofty yarn or a very hard and tightly spun yarn with very different thicknesses but with the same count number.