| No. | Name | Also called | Hook mm | Hook US | Gauge / 4 in | WPI |
|---|---|---|---|---|---|---|
| 0 | Lace | Fingering, 10-count crochet thread | 2.25 | Steel 6, 7, 8 or B-1 | 32–42 dc | 30+ |
| 1 | Super Fine | Sock, Fingering, Baby | 2.25–3.5 | B-1 to E-4 | 21–32 | 14–30 |
| 2 | Fine | Sport, Baby | 3.5–4.5 | E-4 to 7 | 16–20 | 12–18 |
| 3 | Light | DK, Light Worsted | 4.5–5.5 | 7 to I-9 | 12–17 | 11–15 |
| 4 | Medium | Worsted, Afghan, Aran | 5.5–6.5 | I-9 to K-10.5 | 11–14 | 9–12 |
| 5 | Bulky | Chunky, Craft, Rug | 6.5–9 | K-10.5 to M-13 | 8–11 | 6–9 |
| 6 | Super Bulky | Super Bulky, Roving | 9–15 | M-13 to Q | 7–9 | 5–6 |
| 7 | Jumbo | Jumbo, Roving | 15 and up | Q and larger | 6 or fewer | 1–4 |
Gauge / 4 in — how many stitches fit across four inches at that weight. Single crochet throughout except lace, which the Craft Yarn Council quotes in double crochet with a note that a lace gauge is hard to state at all.
WPI — wraps per inch. Wind the yarn around a ruler without stretching it and count the wraps in one inch. It reads one way only: these ranges overlap, so a count of 14 is legitimately three different weights.
The number is a starting point, not a promise. Two yarns both labeled 4 can work up a size apart depending on the fiber and the spin, and the Craft Yarn Council calls all of this guidelines rather than rules.
Always swatch before you trust a weight with a whole blanket. Four inches of yarn now saves ten hours of the wrong size later.