Crochet hook size converter: US, UK & metric side-by-side.
The complete Craft Yarn Council conversion chart — 22 hook sizes from 2.25 mm up to 25 mm. Type any size in any system (mm, US letter, UK number) and the matching row highlights instantly.
Hook converter
| Metric (mm) | US size | UK size |
|---|---|---|
| 2.25 mm | B-1 | 13 |
| 2.50 mm | — | 12 |
| 2.75 mm | C-2 | — |
| 3.0 mm | — | 11 |
| 3.25 mm | D-3 | 10 |
| 3.50 mm | E-4 | 9 |
| 3.75 mm | F-5 | — |
| 4.0 mm | G-6 | 8 |
| 4.50 mm | 7 | 7 |
| 5.0 mm | H-8 | 6 |
| 5.50 mm | I-9 | 5 |
| 6.0 mm | J-10 | 4 |
| 6.50 mm | K-10.5 | 3 |
| 7.0 mm | — | 2 |
| 8.0 mm | L-11 | 0 |
| 9.0 mm | M/N-13 | 00 |
| 10.0 mm | N/P-15 | 000 |
| 12.0 mm | — | — |
| 15.0 mm | P/Q | — |
| 16.0 mm | Q | — |
| 19.0 mm | S | — |
| 25.0 mm | U | — |
Source: Craft Yarn Council standard. Some sizes have no equivalent in another system — shown as «—». UK sizes have been shifted historically; if you have a very old UK pattern, verify against the pattern's stated gauge.
Why crochet hook sizes are so confusing
Three parallel labeling systems developed independently over more than a century. The US used letters (B-1 through Q) that increase in size alphabetically. The UK used numbers that go the opposite way — a UK 14 is a tiny 2.0 mm hook and a UK 000 is a chunky 10.0 mm. Metric millimeters, adopted internationally in the mid-20th century, are the only measurement that means the same thing everywhere.
Most patterns published today list the metric size first, with the US letter in parentheses. Older patterns — especially UK vintage patterns — often list only their local system. The chart above covers every size you're likely to encounter in a modern or vintage English-language pattern.
Which hook do you actually need?
- 3.5 mm (E-4) — amigurumi with worsted or DK yarn, tight fabric so stuffing hides.
- 4.0 mm (G-6) — amigurumi with DK, coasters, tight scarves.
- 5.0 mm (H-8) — the workhorse. Worsted yarn blankets, most beginner patterns, dishcloths.
- 5.5 mm (I-9) — worsted garments with a slightly relaxed drape, granny squares.
- 6.0 mm (J-10) — chunky throws, oversized cardigans, most bulky-yarn projects.
- 9.0 mm (N/M-13) — super-bulky blankets, arm-fatiguing but fast.
A basic beginner kit of 3.5 / 4.0 / 5.0 / 5.5 / 6.0 covers 90% of published crochet patterns.
UK vintage pattern warning
The UK renumbered its hook system in the 1970s. If you're working from a UK pattern published before 1970, the labeled hook size may not match this chart. Rely on the pattern's stated gauge — swatch, measure, and use our gauge helper to find the right metric hook for your yarn.
Related tools
Hook size FAQ
What is the most common crochet hook size?
The 5.0 mm (US H-8, UK 6) is the most commonly recommended size for worsted-weight yarn — the most-used weight in patterns and beginner projects. Amigurumi typically uses 3.5–4.0 mm with worsted or DK yarn to keep the fabric tight enough that stuffing doesn't show through.
Are US and UK crochet hook sizes the same?
No. Completely different systems. US uses letters that increase with size (B-1 through Q). UK uses numbers that DECREASE with size — a UK 14 is 2.0 mm and a UK 000 is 10.0 mm. Metric millimeters are the only truly universal measurement.
What does the letter H mean in crochet?
H is the US letter for a 5.0 mm hook, usually written H-8 (letter plus legacy number). It's the workhorse of worsted-weight crochet and the most common size in beginner kits.
Why do some sizes have no equivalent in another system?
The three systems developed independently. Some millimeter sizes only got a label in one system — 2.5 mm and 3.0 mm have UK numbers but no standard US letter. The «—» dashes mark those gaps.