Knitting Needle & Crochet Hook Sizes
Authority: Craft Yarn Council Standard Hook & Needle Conversion Chart
The Craft Yarn Council publishes standardized charts converting US knitting needle and crochet hook sizes to metric millimeter diameters. Needles run from US 000 (1.5 mm) to US 50 (25 mm); crochet hooks run from US B-1 (2.25 mm) to US T/U/X (25 mm). Because letter and number labels vary slightly by manufacturer, the millimeter size printed on the package is the reliable reference.
| Metric Size | US Knitting Needle | US Crochet Hook |
|---|---|---|
| 1.5 mm | 000 | — |
| 1.75 mm | 00 | — |
| 2.0 mm | 0 | — |
| 2.25 mm | 1 | B-1 |
| 2.75 mm | 2 | C-2 |
| 3.25 mm | 3 | D-3 |
| 3.5 mm | 4 | E-4 |
| 3.75 mm | 5 | F-5 |
| 4.0 mm | 6 | G-6 |
| 4.5 mm | 7 | 7 |
| 5.0 mm | 8 | H-8 |
| 5.5 mm | 9 | I-9 |
| 6.0 mm | 10 | J-10 |
| 6.5 mm | 10½ | K-10½ |
| 8.0 mm | 11 | L-11 |
| 9.0 mm | 13 | M/N-13 |
| 10.0 mm | 15 | N/P-15 |
| 12.75 mm | 17 | — |
| 15.0 mm | 19 | P/Q |
| 19.0 mm | 35 | S |
| 25.0 mm | 50 | T/U/X |
Why Millimeter Size Is the Reliable Reference
US needle and hook sizing uses whole numbers and, for hooks, letters, but those labels are not perfectly standardized between manufacturers -- a US size 7 needle from one company can measure fractionally differently from another brand's size 7. The Craft Yarn Council's own guidance is to rely on the millimeter measurement printed on the package as the accurate figure, treating the US number or letter as a convenient but secondary label.
Steel crochet hooks, used for fine thread work rather than yarn, add a further wrinkle: their numbering runs in reverse of regular hook sizing, so a higher steel hook number indicates a smaller hook rather than a larger one. That inversion is a common source of confusion for crocheters moving between yarn-weight hooks and fine steel thread hooks, which is another reason the metric diameter is treated as the ground truth rather than the number stamped on the hook.
Older and Regional Sizing Systems
Before metric sizing became the common reference, needles were sized under separate national systems, including an old UK/Canadian standard wire-gauge-derived scale that numbered needles in the opposite direction from the US system -- larger UK numbers corresponded to thinner needles, the reverse of the US convention. Vintage patterns and older needle sets can still turn up sized under these older schemes, which is one reason knitters cross-checking an inherited needle or an old pattern are advised to measure the needle's actual diameter rather than trust the printed number alone.
Today, US and metric sizes are what appear on virtually all current commercial needles and hooks sold in North America, with the metric figure serving as the internationally consistent constant across both.