When we talk about yarn weight, there is a standardized table of yarn types corresponding with their weights. Have a look
Not so much in India, but overseas yarns usually come with a label indicating a number such as the one mentioned on the top axis of the table. Based on the number, you can get details of the yarn type, gauge and recommended needle size. Have a look at the label on the yarn in the picture below
As per the table above, the number “4” that is mentioned on the label tells me that this is a worsted weight/aran weight yarn for which the recommended needle size is 4.5-5.5 mm and Gauge is 16-20 stitches over 4 inches. With the help of the yarn weight, it is possible to find out the correct needle, the recommended gauge, even how much yarn a project will require. It is also helpful in case you want to substitute yarn. Knowing just one variable in the table will give information about the remaining things. For example, have a look at the yarn below
This one does not mention a yarn weight. For this kind of yarn, look for the recommended needle size. In India, yarn manufacturers often provide a recommended needle size on the label. If you check the table, needle size 3.75 mm is recommended for the number “2” and “3” yarn weights, which have a gauge of 21 to 26 stitches per 4 inches between them.
It’s pretty simple actually. If you know any one thing about a yarn, you can figure out everything else about it using this table. Just like magic!
I have found this table to be one of the most handy tools in knitting. I suggest you bookmark this page because you’re going to need to refer to this table again and again.