Crochet Hook Size Chart: US, UK and Metric Conversions
The millimetre measurement is the real size. Everything else is a label. A US “G” hook is 4 mm from one brand and 4.25 mm from another, and the old UK numbers run backwards from the US ones. If a pattern gives you a letter, find the millimetre equivalent below and use that.
The conversion chart
| Metric | US | UK / Canada (old) | Common use |
|---|---|---|---|
| 2.0 mm | — | 14 | Thread, fine lace |
| 2.25 mm | B-1 | 13 | Lace, thread |
| 2.5 mm | — | 12 | Lace |
| 2.75 mm | C-2 | — | Amigurumi in fine yarn |
| 3.0 mm | — | 11 | Fine work |
| 3.25 mm | D-3 | 10 | Sock/fingering yarn |
| 3.5 mm | E-4 | 9 | Amigurumi in DK, fine garments |
| 3.75 mm | F-5 | — | Amigurumi, tight fabric |
| 4.0 mm | G-6 | 8 | DK garments, baby hats |
| 4.5 mm | 7 | 7 | DK, light worsted |
| 5.0 mm | H-8 | 6 | The most-used hook. Worsted-weight everything. |
| 5.5 mm | I-9 | 5 | Worsted, loose fabric |
| 6.0 mm | J-10 | 4 | Worsted to aran |
| 6.5 mm | K-10½ | 3 | Aran, light bulky |
| 7.0 mm | — | 2 | Bulky |
| 8.0 mm | L-11 | 0 | Bulky |
| 9.0 mm | M/N-13 | 00 | Super bulky |
| 10.0 mm | N/P-15 | 000 | Super bulky |
| 12.0 mm | — | — | Super bulky |
| 15.0 mm | P/Q | — | Jumbo |
| 16.0 mm | Q | — | Jumbo |
| 19.0 mm | S | — | Jumbo, arm-crochet |
Why the US letters cannot be trusted
Three separate problems, all real, all still present in 2026:
The letter and the number disagree between brands. “G” is 4.0 mm on most hooks and 4.25 mm on some. “M” and “N” both appear on 9 mm hooks. “N” and “P” both appear on 10 mm hooks. Manufacturers never agreed a single mapping, and there is no body that could force one.
The UK system runs the opposite way. Bigger UK number means smaller hook. UK 14 is 2 mm; UK 000 is 10 mm. If you are following a British pattern from before about 2000, this catches almost everyone once.
The old UK numbers overlap the modern US numbers. A pattern that just says “size 7 hook” is ambiguous: US 7 is 4.5 mm, and UK 7 is also 4.5 mm — a coincidence that does not hold anywhere else on the chart. Size 4 is 6 mm in the UK and does not exist in the US system.
The fix is one habit: when you write down a hook size, write the millimetres. When a pattern gives you a letter, convert it once and note it in the margin.
Which hook for baby projects
| Project | Yarn | Hook |
|---|---|---|
| Baby blanket, standard drape | Worsted (4) | 5.0–5.5 mm |
| Baby blanket, softer and looser | Worsted (4) | 6.0 mm |
| Baby hat | DK (3) | 4.0–4.5 mm |
| Booties | DK (3) | 3.5–4.0 mm |
| Amigurumi toy | DK (3) | 3.0–3.5 mm — deliberately smaller than the label says |
| Cardigan | Sport (2) | 3.5–4.0 mm |
Amigurumi is the deliberate exception. You go one or two sizes below what the yarn label recommends, because you want a fabric tight enough that the stuffing does not show through the stitches. It is harder on the hands and it is the whole technique.
What most hook charts get wrong
They present the US letters as if they were sizes. They are brand labels that happen to correlate with size.
They give a single UK number for every metric size. Several metric sizes have no UK equivalent at all — 2.75, 3.75 and 5.5 mm among them. Charts that fill those cells in are guessing.
They ignore steel hooks entirely, which use their own separate numbering that runs backwards — a steel size 14 is 0.75 mm, far smaller than a steel size 00 at 3.5 mm. If you are working with crochet thread rather than yarn, you are in a different numbering system and this chart does not apply.
Frequently asked questions
What is the most common crochet hook size? 5.0 mm (US H-8). It pairs with worsted-weight yarn, which is the most common yarn, so it is the single most useful hook to own.
Does hook size change the finished size? Yes, substantially. Going up one hook size on a 30-inch blanket typically adds 1–2 inches of width. This is the fastest way to adjust a project that is coming out too small — before ripping anything back, try the next hook up.
What hook do I use if the pattern doesn’t say? Use the size printed on the yarn label, then swatch. The label recommendation is a starting point chosen by the yarn manufacturer, and it is usually a good one.
Are ergonomic hooks a different size? No. The handle is different; the hook shaft is the stated millimetre size. If you crochet for more than an hour at a time, they are worth it.
Why do some hooks have two letters, like M/N-13? Because the manufacturers never agreed. Read the millimetres stamped on the shaft.