Convert between grams of yarn and yards using the ball band.
Uses the yards/grams ratio printed on the ball band.
Yarn is sold by weight but patterns often list the length needed, so it helps to convert between them. The ball band shows the yards and the grams in one ball, and dividing the yards by the grams gives the number of yards per gram. Multiply that by the grams you have to find how many yards are left.
For example, a ball of 220 yards and 100 grams has 2.2 yards per gram, so 60 grams of leftover yarn is about 132 yards. A small kitchen scale makes this quick, and it is a handy way to see whether you have enough yarn to finish a project before you run out.
Yarns of the same weight category can have very different lengths per gram, depending on the fiber, so compare the yardage a pattern asks for rather than the number of balls or grams. Buy all the yarn for a project from the same dye lot, since colors can vary slightly between lots.
Weigh a new ball before you begin and note the weight, so you can tell how much of it you have used at any time. Wind leftover yarn into small balls and label each with its fiber, weight, and the remaining yardage for later projects.