Needle and hook sizing systems vary by country and manufacturer. The metric millimeter measurement is the universal reference — if your pattern specifies a US size or UK old number, use the mm column to find the exact equivalent. Always swatch before starting a project, as needle and hook brands vary slightly in actual diameter even at the same labeled size.
Knitting needle sizes
US sizes run from 0 (2.0 mm) to 50 (25.0 mm). The old UK/Canada system counts in reverse — a UK 14 is the smallest (2.0 mm) and UK 000 is among the largest. Many older British and Canadian patterns use the UK number; convert via the mm column.
| US Size | Metric (mm) | UK / Canada (old) |
|---|---|---|
| 0 | 2.0 | 14 |
| 1 | 2.25 | 13 |
| 1.5 | 2.5 | — |
| 2 | 2.75 | 12 |
| 3 | 3.25 | 10 |
| 4 | 3.5 | — |
| 5 | 3.75 | 9 |
| 6 | 4.0 | 8 |
| 7 | 4.5 | 7 |
| 8 | 5.0 | 6 |
| 9 | 5.5 | 5 |
| 10 | 6.0 | 4 |
| 10.5 | 6.5 | 3 |
| 11 | 8.0 | 0 |
| 13 | 9.0 | 00 |
| 15 | 10.0 | 000 |
| 17 | 12.75 | — |
| 19 | 15.0 | — |
| 35 | 19.0 | — |
| 50 | 25.0 | — |
Crochet hook sizes
US crochet hooks use a letter/number system (B-1 through S). Sizes smaller than B-1 (0.6–1.9 mm) are used for thread crochet and labeled by number only (14 through 6). The UK old system counts downward, similar to the knitting needle system.
| US Size | Metric (mm) | UK / Canada (old) |
|---|---|---|
| B-1 | 2.25 | 13 |
| C-2 | 2.75 | 12 |
| D-3 | 3.25 | 10 |
| E-4 | 3.5 | 9 |
| F-5 | 3.75 | 8 |
| G-6 | 4.0 | 8 |
| 7 | 4.5 | 7 |
| H-8 | 5.0 | 6 |
| I-9 | 5.5 | 5 |
| J-10 | 6.0 | 4 |
| K-10.5 | 6.5 | 3 |
| L-11 | 8.0 | 0 |
| M/N-13 | 9.0 | 00 |
| N/P-15 | 10.0 | 000 |
| P/Q | 15.0 | — |
| S | 19.0 | — |
Yarn weight and needle / hook recommendations
Craft Yarn Council (CYC) defines 8 standard weight categories (0–7). The needle and hook ranges below are the recommended starting points — your gauge swatch determines the actual size for your project.
WPI = wraps per inch. Wind yarn around a ruler for one inch and count the strands.
| CYC # / Name | Knitting needle (mm) | Crochet hook (mm) | WPI | Examples |
|---|---|---|---|---|
| 0 — Lace | 1.5–2.25 | 1.6–2.25 | 30–40+ | Cobweb, thread |
| 1 — Super Fine | 2.25–3.25 | 2.25–3.5 | 20–30 | Fingering, sock, baby |
| 2 — Fine | 3.25–3.75 | 3.5–4.5 | 15–20 | Sport, baby |
| 3 — Light | 3.75–4.5 | 4.5–5.5 | 12–15 | DK, light worsted |
| 4 — Medium | 4.5–5.5 | 5.5–6.5 | 9–12 | Worsted, aran |
| 5 — Bulky | 5.5–8.0 | 6.5–9.0 | 6–9 | Chunky, craft, rug |
| 6 — Super Bulky | 8.0–12.75 | 9.0–15.0 | 4–6 | Bulky, roving |
| 7 — Jumbo | 12.75+ | 15.0+ | fewer than 4 | Jumbo roving, arm knitting |
Reading a pattern — sizing tips
US pattern with no mm given. Look up the US size in the knitting needle or crochet hook table above to find the mm equivalent. Buy the closest metric size available — most modern needles and hooks are sold by mm.
Old UK/Canada pattern. Older patterns (pre-1970s) use the UK old number. Find it in the UK/Canada column and read across to metric. UK 8 = 4.0 mm, not US 8 (5.0 mm).
Pattern gauge doesn't match. Go up a needle or hook size if your gauge is too tight (fewer stitches than specified per inch); go down a size if too loose (more stitches). A half-size change in needle diameter is often enough to shift gauge by one stitch.
For the interactive needle converter, see the Knitting Needle Size Converter →, the Crochet Hook Size Converter →, and the Yarn Weight Guide →.