Demystifying WPI

So you’ve bought a skein of hand spun yarn and it has some mystery code on it: “WPI”. What on Earth is it, what does it mean, and how is it going to help you?

Quite simply WPI stands for “Wraps Per Inch” and it’s the way that spinners calculate the weight of the yarn they have spun. But not only that, it is also incredibly useful if you’ve lost the tag for a ball of yarn and can’t remember what weight it was. Rather than blindly guessing, WPI will tell you exactly.

(Note: at this point it is useful to mention that when I say weight I don’t mean how heavy your ball of yarn is, you’ll need a set of scales for that! Rather I mean calculating whether your yarn is lace weight or super bulky)

Basically all you need to do is wrap your yarn around an object which has one inch marked on it, say a ruler, a pencil, or a specially made WPI gauge. Personally I use a little steel rule which I “acquired” from my husband’s desk (don’t worry, he’s got another!). Then the more wraps of your yarn that are required to fill up the whole of the marked inch, the finer the weight of your yarn. It really is quite simple!

Once you know your WPI you can then translate it into a yarn weight. There are several different tables available (some which I agree with and some which I definitely don’t!), so here is the table I use:

WPI Yarn Weight
>35 Lace
29-34 Heavy lace
23-28 Light fingering
19-22 Fingering
15-18 Sport
12-14 DK
9-11 Worsted
7-8 Bulky
<6 Super bulky

I have also written this out as a handy pdf which you can see here:  Yarn Weight from WPI.

And for those who prefer a video tutorial, I filmed myself measuring the WPI of one of my latest skeins. I hope you find it helpful!