We have all seen yarn advertized, usually for weaving and on cones, with thicknesses quoted as 2/8 or 3/10. What does this mean?

First you have to realize that there are a number of systems.

The metric is easiest, so let's discuss that first. A metric figure will be given as 2/8 nm. One nm equals 1,000 metres of yarn per kilogram (1,000 m/kg). Thus a 1 nm yarn will contain 1000 metres per kilogram, or 50 metres in 50 grams. A 1/8 nm yarn means that the yarn has been spun 8 times longer than the standard (and therefore finer), and you will therefore get 8,000 metres per kilogram.

The first number is the number of plies. Thus a 2/8 yarn has two plies. The 8 means that the basic yarn was spun to 8,000 m/kg, but it was then spun into a 2 ply, and so it now has only 4,000 m/kg. A 3/8 will have 2,666 m/kg.

With the metric system, 1 nm always equals 1,000 m/kg, regardless of the yarn fibre.

Not so with the imperial system. First you have to determine the fibre. A count of one gives the number of yards per pound, but it depends on the yarn. See the table below.

Worsted wool is nothing to do with worsted weight yarn. Worsted wool is wool which is carded and combed so that all the fibres are parallel. Woolen measure or Yorkshire wool is carded but not combed, so is a little rougher. Worsted wool is usually very fine and used for suits and fine fabric. Hand knitting yarn is usually woolen type yarn. When quoting wool some manufacturers specify "worsted" or "woolen". Most do not!

Getting complicated isn't it? So lets say we have a hand knitting woolen yarn with an count of 3/8. The 8 means it is spun 8 times longer than standard, or 8 x 256 = 2,048 yards per pound (2,048 yds/lb) The 3 means it is 3 ply, so the finished yarn has 2,048/3 = 682 yards per pound. This is a chunky weight yarn (roughly). A 2/10 yarn will have 2,560 yds/lb divided by 2 plies = 1,280 yds/lb. This will be in the DK to worsted weight range.

Now, cottons have a base count of 840 yds/lb. Just to complicate matters, cotton is usually quoted with the count first and the ply last! (Nobody said this would be easy!) So a 10/2 cotton will have 8,400 yds/lb divided by 2 plies = 4,200 yds/lb. This is a "three ply baby" type weight.

Finally, you have to remember that hand knitting yarns vary a lot in weight per yard, from brand to brand, and type to type. For example a superwash wool is heavier than a regular wool. With this in mind we can produce a table for various counts of wool.