Knitting Needle and Crochet Hook Sizes: US and Metric (mm)
Choose needle or hook, then the size you know, US or metric: the calculator gives the equivalent from the Craft Yarn Council chart.
Size in millimeters
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How the calculation works
US patterns name knitting needles by a number and crochet hooks by a letter, usually followed by a number (H-8). Needle packages and patterns from outside the US give the diameter in millimeters. The calculator reads the Craft Yarn Council chart, which pairs the two.
Some US sizes match more than one diameter (US 6: 4 mm or 4.25 mm; US 9: 5.25 or 5.5 mm), and some diameters have no US size (3 mm, 7 mm). The calculator shows them as the chart lists them.
Sources:
Sources consulted November 10, 2026
Sizes in millimeters and US sizes (Craft Yarn Council); "—": no equivalent
| Diameter | Knitting needle (US) | Crochet hook (US) |
|---|---|---|
| 1.5 mm | 000 | — |
| 1.75 mm | 00 | — |
| 2 mm | 0 | — |
| 2.25 mm | 1 | B-1 |
| 2.5 mm | — | — |
| 2.75 mm | 2 | C-2 |
| 3 mm | — | — |
| 3.125 mm | 3 | D |
| 3.25 mm | 3 | D-3 |
| 3.5 mm | 4 | E-4 |
| 3.75 mm | 5 | F-5 |
| 4 mm | 6 | G-6 |
| 4.25 mm | 6 | G |
| 4.5 mm | 7 | 7 |
| 5 mm | 8 | H-8 |
| 5.25 mm | 9 | I |
| 5.5 mm | 9 | I-9 |
| 5.75 mm | 10 | J |
| 6 mm | 10 | J-10 |
| 6.5 mm | 10½ | K-10½ |
| 7 mm | — | — |
| 8 mm | 11 | L-11 |
| 9 mm | 13 | M/N-13 |
| 10 mm | 15 | N/P-15 |
| 11.5 mm | — | P-16 |
| 12 mm | — | — |
| 12.5 mm | 17 | — |
| 12.75 mm | 17 | — |
| 15 mm | 19 | P/Q |
| 15.75 mm | — | Q |
| 16 mm | — | Q |
| 19 mm | 35 | S |
| 25 mm | 50 | T/U/X |
| 30 mm | — | T/X |
| 35 mm | 70 | — |
Limitations
- The Craft Yarn Council notes that US letters and numbers vary from one manufacturer to another: rely on the millimeter size printed on the package.
- Whatever the size, knit or crochet a gauge swatch and compare it to the pattern's gauge: the swatch decides the right needle or hook size.
- Steel crochet hooks, used for thread and lace-weight yarn, follow a separate, reversed numbering (the higher the number, the smaller the hook): they are not in this chart.
- Older UK and Canadian needle sizes are not in this chart either (in that system, too, a higher number means a thinner needle).
Results are estimates. Always check your pattern's instructions and the product label or seller's information.
Frequently asked questions
How many mm is a US 8 knitting needle?
5 mm, according to the Craft Yarn Council chart.
What size is an H-8 crochet hook?
5 mm. US letters can differ between brands: check the millimeter size on the package.
Why does one US size match two diameters?
The Craft Yarn Council chart sometimes gives the same US size to two close diameters, for example 4 mm and 4.25 mm for US 6. Use the one your pattern calls for, or the one that gives you the right gauge.
Are steel crochet hooks in this chart?
No. Steel hooks are numbered the other way around: the higher the number, the smaller the hook. The Craft Yarn Council lists them separately, from #14 (0.9 mm) to 00 (2.7 mm).