Crochet Hook Size Converter
Crochet hooks are labeled three different ways: a metric millimeter size, a US letter and number, and an older UK and Canadian number. A pattern from one country can leave you guessing what hook you actually need. Pick the size you know below and this converter shows you the exact equivalent in the other systems. The values come from the Craft Yarn Council standard, the official US sizing body.
Letters and numbers vary a little by brand, so treat the millimeter value as the true one. When in doubt, read the mm stamped on your hook.
Full crochet hook size chart
Every common yarn hook size, from the small 2.25 mm all the way up to jumbo. A blank means that source lists no standard label for that size, so we leave it honest rather than guessing.
| Metric (mm) | US size | Old UK / Canadian |
|---|---|---|
| 2.25 | B-1 | 13 |
| 2.75 | C-2 | 12 |
| 3.25 | D-3 | 10 |
| 3.5 | E-4 | |
| 3.75 | F-5 | 9 |
| 4.0 | G-6 | 8 |
| 4.5 | 7 | |
| 5.0 | H-8 | 6 |
| 5.5 | I-9 | 5 |
| 6.0 | J-10 | 4 |
| 6.5 | K-10.5 | 3 |
| 8.0 | L-11 | 0 |
| 9.0 | M/N-13 | 00 |
| 10.0 | N/P-15 | 000 |
| 11.5 | P-16 | |
| 15.0 | P/Q | |
| 16.0 | Q | |
| 19.0 | S | |
| 25.0 | T/U/X |
- UK numbers run backwards. In the US system a bigger letter means a bigger hook. In the old UK and Canadian system a bigger number means a smaller hook, so UK 14 is tiny and UK 000 is large. Never convert a bare number without knowing which system wrote it.
- Letters are not standardized. The Craft Yarn Council warns that letter sizing varies by company. A G can be 4.0 mm on one brand and 4.25 mm on another. The millimeter number is the only measurement that means the same thing everywhere.
Steel (thread) hooks are a different system
Steel hooks are the tiny hooks used for thread crochet, doilies, and lace. Their US numbering runs the opposite way to regular hooks: a higher steel number means a smaller hook, and a "US 2" steel hook is nothing like a "US 2" yarn hook. If you are working with thread rather than yarn, use this separate chart.
| Metric (mm) | US steel | UK steel |
|---|---|---|
| 2.25 | 2 | 1.5 |
| 2.0 | 4 | 2.5 |
| 1.8 | 6 | 3.5 |
| 1.65 | 7 | 4 |
| 1.5 | 8 | 4.5 |
| 1.4 | 9 | 5 |
| 1.3 | 10 | 5.5 |
| 1.1 | 11 | 6 |
| 1.0 | 12 | 6.5 |
| 0.85 | 13 | 7 |
| 0.75 | 14 |
Just getting started with hooks and yarn?
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Which hook goes with which yarn?
Yarn labels suggest a hook range, and it is the fastest way to pick a starting hook. These are the common pairings, though your pattern and your gauge always have the final say.
- Super fine (fingering, sock): about 2.25 to 3.5 mm (B-1 to E-4).
- Fine (sport, baby): about 3.5 to 4.5 mm (E-4 to 7).
- Light (DK): about 4.5 to 5.5 mm (7 to I-9).
- Medium (worsted, aran): about 5.5 to 6.5 mm (I-9 to K-10.5).
- Bulky (chunky): about 6.5 to 9 mm (K-10.5 to M/N-13).
- Super bulky: about 9 to 15 mm (M/N-13 to P/Q).
Where to go next
- How much yarn do I need? A free calculator for any project.
- Free crochet abbreviations and symbols cheat sheet for reading any pattern.
- How to read a crochet pattern, including gauge and hook notes.
- Crochet gift deadline calculator to see what you can finish in time.
- Browse all our free crochet patterns.
Frequently asked questions
- What size is a 5.5 mm crochet hook?
- A 5.5 mm hook is a US size I-9, and a 5 in the old UK and Canadian numbering. The millimeter value is the reliable one.
- What is a US H crochet hook in mm?
- A US H-8 hook is 5.0 mm, one of the most common beginner sizes, and a good match for worsted weight yarn.
- Do UK and US crochet hook sizes run the same direction?
- No. US sizes get bigger as the letter climbs, but old UK numbers get smaller as the number climbs, so UK 14 is tiny and UK 000 is large. Always know which system a number came from before you convert it.
- Where do these numbers come from?
- The millimeter and US columns follow the Craft Yarn Council standard, the official US sizing body, and the UK and steel columns are corroborated against it. Because letters vary by brand, trust the mm on your own hook. You can browse our free patterns or see our full-color beginner guides on Amazon.