A yarn label is both a buying reference and a record you may need months later. Before winding a hank or discarding a ball band, save the information that lets you identify the yarn, calculate a quantity and care for the finished piece.
Copy the details that answer different questions
Record the product name, fibre composition, yarn-weight category if given, net mass, length, shade identifier and dye lot where supplied. Keep the care instructions too. A thickness category describes a range; grams tell you how much the ball weighs; metres or yards tell you its length. Those numbers are not interchangeable.
Check whether a printed gauge and tool symbol refers to knitting or crochet. It is a reference for a particular sample, not a promise about your chosen stitch. Use your own crochet swatch for the calculations on this site.
Compare length before counting balls
Imagine yarn A comes in 100 g balls containing 220 m and yarn B in 50 g balls containing 110 m. They have the same listed length per gram, but B needs twice as many balls for the same length. That arithmetic does not establish that the yarns have identical fibre, thickness, drape or suitability.
For a hypothetical 660 m requirement, the label arithmetic gives three balls of A or six of B. If the displayed prices were £6 and £3.50 respectively, the totals would be £18 and £21 before delivery. These are invented comparison figures, not live prices or product recommendations. Add your project's chosen allowance before rounding to whole balls if it is not already included in the requirement.
Whole balls = round up (required metres ÷ metres per ball)
Keep shade and batch information together
A descriptive name such as “ocean blue” is not enough to identify a product reliably. Keep the brand, line and shade code together, plus the dye lot if there is one. When buying additional yarn, compare those details and inspect it beside the existing material under the same light.
Retain a short strand with the label in your project notes. That gives you a physical comparison later and avoids relying entirely on a photograph whose colour may change with lighting or display settings. Do not assume that two different product lines use the same shade merely because their names match.
Save care information for the finished item
Use the manufacturer's explanation for any unfamiliar care symbol rather than guessing what it means. If a project combines several yarns, choose a treatment compatible with every material and check it on a combined sample. Give the relevant care instructions to anyone receiving the finished item.
A compact record might read: product and shade; batch; composition; 100 g / 220 m; hook used; washed gauge; care instructions; quantity obtained. Keep it with the project checklist. For substitution, move on to comparing yarns through length and a swatch.
References: Craft Yarn Council: yarn label information and Lion Brand: label and care information.