You can do it by weight if you have a postal or baking scale. Grams are easier to work with than ounces. So weight the skein(s) before beginning and then after you're through for the day and subtract the 2nd from the first. Let's say it's 20 grams. Go back to the label and divide the number of yards in the skein by the number of grams. That will give you how many yards per gram let's say it's sock yarn, 200 yards for 50 grams. Every gram would be 4 yards. So 20 grams times 4 yards would mean you'd knitted 80 yards that day.
