How much yarn do I need for a sweater?
A reliable way to estimate yarn from a weighed swatch, a worked example for a classic sweater and how much to add as a reserve.
- Weigh your swatch: grams ÷ area gives the weight of 1 cm² of your fabric.
- Add up the area of all the pieces of the garment.
- Area × weight per cm² = yarn needed; add 10–15% as a reserve.
- Buy all skeins from the same dye lot.
Why the label is not enough
The label tells you the weight and the length of a skein, but not how much of it your sweater will use. The same yarn knitted on different needles, in a different stitch or by a different knitter can use noticeably different amounts. Cables and textured stitches use more yarn than stockinette; lace uses less.
The most reliable source of information is the fabric you will actually knit — your swatch.
Weigh the swatch
Knit the swatch in the stitch of the garment, wash it and let it dry, then weigh it on a kitchen scale with 1 g accuracy (a jewellery scale is even better). Divide its weight by its area.
Example: a swatch of 15 × 15 cm has an area of 225 cm² and weighs 9 g. Its weight per area is 9 ÷ 225 = 0.04 g per cm².
Add up the area of the pieces
Treat each piece as a rectangle — the shaping removes a little, the seams and the ribbing add a little, and it roughly evens out. For a classic sweater:
- front 50 × 60 cm = 3000 cm²,
- back 50 × 60 cm = 3000 cm²,
- two sleeves, average width 30 cm × length 45 cm = 2 × 1350 = 2700 cm²,
- neckband and finishing about 300 cm².
Together: 9000 cm².
Calculate and add a reserve
Multiply the area by the weight per cm²: 9000 × 0.04 = 360 g. Add a reserve of 10–15% for swatching, seaming and the unexpected: 360 g + 10% ≈ 400 g. With skeins of 100 g, that is four skeins.
If you prefer to think in metres, use the label: a 100 g skein with 200 m means about 800 m for 400 g. For colourwork, estimate the share of each colour on the chart and split the total accordingly.
Buy from one dye lot
Skeins dyed in different batches can differ slightly in colour, and the difference often shows only once they sit next to each other in the finished sweater. Buy all the yarn for a project at once and check that the dye lot number on the labels is the same. If you have to mix lots, alternate them every two rows for a few centimetres so that the change is invisible.
The yarn calculator in KnitLab Studio
In KnitLab you weigh a small swatch, enter its size and the size of the project, and the yarn calculator estimates how much yarn you need — for a sweater, a hat or a scarf. Together with the garment constructor, which calculates the pieces from your gauge and measurements, it gives you a complete picture of the project before you buy the yarn.
Questions about this topic
How much extra yarn should I buy?
About 10–15% more than the calculated amount — usually one extra skein for a sweater.
Why does the same pattern need different amounts of yarn for different knitters?
Because tension differs. A looser knitter makes larger stitches and uses more yarn per stitch; that is why the calculation should start from your own swatch.
What if I run out of yarn?
Try to find a skein from the same dye lot. If that is not possible, use the new lot in the ribbing or the neckband, or alternate the two lots every two rows so that the change does not show.