The scale
Yarn weight has nothing to do with how much a skein weighs. It is the thickness of the strand, named on a scale that runs from lace at the fine end to super bulky at the thick end. The Craft Yarn Council numbers them 0 to 7; most ball bands, and every page on this site, use the names.
| Weight | Also called | Stitches per 4" (stockinette) | Needles | Typical 100 g skein |
|---|---|---|---|---|
| Lace | 2-ply, cobweb | 32–40+ | US 000–3 | 800–1,500 yd |
| Fingering | 4-ply, sock, super fine | 27–32 | US 1–3 | 400–450 yd |
| Sport | 5-ply, fine | 24–26 | US 3–5 | 300–350 yd |
| DK | 8-ply, double knitting, light | 21–24 | US 5–7 | 250–290 yd |
| Worsted | 10-ply, medium | 16–20 | US 7–9 | 200–220 yd |
| Aran | heavy worsted | 16–18 | US 8–9 | 160–200 yd |
| Chunky | bulky | 12–15 | US 9–11 | 100–140 yd |
| Bulky / super bulky | jumbo, roving | 6–11 | US 11–17 | 50–100 yd |
The gauge column is the one that matters. Two yarns of the same "weight" from different mills can differ by a stitch an inch, which over a sweater is a whole size — so a pattern's gauge is the number to match, and the weight name is only how you find candidates.
What each weight is for
Lace is for shawls and wraps, and for holding with another yarn to add a halo of mohair or a glint of silk. A single 50 g skein of laceweight is often a whole shawl. It blocks open dramatically; a lace piece looks like a rag until it has been stretched and pinned.
Fingering is the most versatile fine weight: socks, lightweight sweaters, most shawl patterns, colourwork. A 100 g skein is a pair of adult socks. For socks, choose a plied superwash with nylon; for shawls, anything with drape.
Sport and DK are the middle of the range and the weights the most patterns are written for — baby garments, year-round sweaters, hats, mittens. DK is quick enough to finish a sweater and fine enough that the sweater is not a coat.
Worsted and aran are the weights to learn on and the ones most sweater, hat, blanket and mitten patterns assume. About 200 yards to 100 g; an adult sweater is five to seven skeins.
Chunky and bulky are fast. A hat is an evening, a cowl an hour, a blanket a weekend. Yardage per skein is low, so count skeins by the pattern's total yardage rather than by weight.
Converting between weights
You can knit a pattern in a different weight than it calls for, but not by simply swapping yarn: the stitch counts assume the pattern's gauge. Holding two strands of a finer yarn together approximates the next weight up or two — two strands of fingering knit roughly as DK, two of DK roughly as worsted-to-aran — and it is the usual way to get a laceweight halo into a sweater. Always swatch the held combination.
Reading a ball band
The band gives the weight name, the recommended needle size and the gauge the mill got with it, the yardage and the grams. The gauge on the band is a starting point, not a rule: knit a 6" swatch, wash it as you will wash the garment, and measure the middle four inches. That number, not the band's, is what you compare with the pattern.