What are wraps per inch and how do I measure them?

WPI is one of those mysterious abbreviations that yarnies toss about to the bamboozlement of the rest of us! In fact it's simply a way of categorising the weight of a yarn.

I don't know how the rest of the world gets on. If you're English it can be very confusing I was taught 4ply and Double Knitting. That left me wondering what on earth Lace weight and Fingering was. Then there are crochet thread weights 3, 5, and 8; as well as 10,20,30 etc. So compared to that WPI starts to seem really sensible.

There is always a catch! Your WPI will depend on how much tension you use. The way you calculate wraps per inch is merely to wrap it around something and count the number of wraps in an inch! The width (and length) of a piece of yarn depends on how much tension is put on the threads. It really is a case of 'how longs a piece of string?!!

If you search for WPI gauge tools, I'm sure you'll find plenty but all you really need is a ruler. The best way to work out your WPI is to lay the threads over the ruler or lightly wrap it.
Don't just wrap an inch as any variations in the thickness and the wrapping process will effect your count. So wrap a number of inches laying the strands snugly next to each other.

If it's a very fine yarn you will only need to wrap a couple of inches, but if it's very chunky you'll need to choose a much larger distance.
Count the strands and divide by the number of inches you've wrapped.
So I've got my count, what now? 
Well now you can identify the yarn weight. Try using the Craft Yarn Council chart that you'll find here. If your yarn has lost it's label you now stand a better chance of identifying it! Perhaps you are thinking of combining two different yarns together in the same project, or are using up oddments. You can now ensure that all your yarns are a similar size.

This yarn is from a charity shop. All the label tells me is the name of the yarn and who made it. I can find very little information about it on line. But knowing it has 5WPI I can search for patterns using Super Bulky yarn. That will keep me out of trouble for hours!

Fastening off...