When working on a crochet project, it is very important to use the appropriate yarn size, because it greatly influences the final result. Yarn size, or yarn weight tells us how thick the yarn actually is.
But sometimes, the label does not suggest the size/weight, or you acquire yarn without a label, and then it is important to know the thickness as to determine the right size. During all these past years of crocheting, I can recognize sizes just by looking and feeling the yarn, but it has sporadically happened to me, to not being quite able to determine the size when it comes to chunkier yarns, especially sizes 5 and 6.
The solution for this is immensely easy.
To determine the size of yarn or the Wraps Per Inch (WPI) you need yarn (of course), a ruler (or tape measure) and an ordinary HB pencil.
Start wrapping the yarn around the pencil until the wraps measure an inch. That is how you determine the size. Above you have the table that shows how many wraps per sizes.
Here it is important to know that when wrapping, the wraps must not overlap, there shouldn't be any gaps, and also the tension must not be too strong.
I hope you find this useful. Happy crochet time!