How can I tell the weight of a yarn, when the label is missing? Thanks.
Do you mean weight as in thickness of the yarn, or the weight in grams or ounces of the whole skein? There’s a big difference.
If, as suzeeq says, you mean the weight of the entire skein/ball/hank, if you have a food scale at home, or know someone who does, that is a great way to go because it’ll weigh such small amounts and in ounces or grams. But if you mean weight, as in lace, sport, worsted, fingering, bulky, etc., then some people love the wraps-per-inch method. I don’t, because I don’t know how tightly I’m wrapping as opposed to the next person, and you have to use a specific thickness of the dowel for it (there’s a tool just for this, actually). What I would do, if you live anywhere near an LYS or Michael’s, Joann’s, etc., is cut off a few inches and take it with you and hold it up against various yarns and see what it’s most like.
To do wraps per inch you can use anything as your tool,a pencil, knitting needle, etc. What you are looking at is how thick (wide) the yarn is.
You could cut the yarn in to short lengths and lay them side by side. I find that a US ruler marked off by inches is a great tool. Gently wrap the yarn around your tool so that there is no tension on the yarn. Wrap (gentely lay the yarn around) two inches and then count the number of wraps and divide by 2. I think this is a little more exact then wrapping only one inch.
You could take a small piece of plastic mark off 1 inch and attach it to you key chain and always have a way to check yarn weight.