A crochet hook conversion chart lines up the four sizing systems you’ll run into: millimeters, US letter, US number, and UK/old-UK numbering. Millimeters are the anchor — every brand agrees on the mm measurement even when their letter or number stamp differs, so that’s the column to check first when you’re converting a pattern.
Below you’ll find the fastest lookups for the sizes people search most, the full bidirectional table, a quick yarn-weight match, and a printable option.
Quick Conversions
The direct answers for the sizes crocheters look up most often:
- 4 mm = US G-6. The standard DK-to-worsted hook.
- 5 mm = US H-8. The most common beginner and worsted-weight size.
- 5.5 mm = US I-9. A common step-up size for slightly looser gauge.
- 6 mm = US J-10. The usual choice for bulky yarn and quick blankets.
- US size 7 = 4.5 mm. No standard US letter is assigned to this size — brands mark it numerically.
- 3.5 mm = US E-4. A common size for lighter DK-weight projects.
- 9 mm = US M/N-13. A jumbo size for super bulky yarn and fast makes.
[VERIFY: cross-check each pairing above against a current niche chart before publishing, since a small number of brands vary slightly on the mid-range letters.]
Full Crochet Hook Conversion Chart
Use the mm column as your anchor, then read across to find the matching US or UK size. UK and old-UK/Canadian numbering runs backward from US sizing — the number gets smaller as the hook gets bigger, the opposite of the US system.
| Metric (mm) | US letter | US number | UK / old-UK |
|---|---|---|---|
| 2.00 mm | B | 1 | 14 |
| 2.25 mm | B | 1 | 13 |
| 2.75 mm | C | 2 | 12 |
| 3.25 mm | D | 3 | 10 |
| 3.5 mm | E | 4 | 9 |
| 3.75 mm | F | 5 | 8 |
| 4.0 mm | G | 6 | 8 |
| 4.5 mm | no standard letter | 7 | 7 |
| 5.0 mm | H | 8 | 6 |
| 5.5 mm | I | 9 | 5 |
| 6.0 mm | J | 10 | 4 |
| 6.5 mm | K | 10½ | 3 |
| 8.0 mm | L | 11 | 0 |
| 9.0 mm | M/N | 13 | 00 |
| 10.0 mm | N/P | 15 | 000 |
Two sizes — 4.5 mm and 6.5 mm’s near-neighbor gap aside — never got a consistent US letter across every manufacturer, so 4.5 mm is usually just called “size 7.” When in doubt, convert by mm rather than trust a printed letter. [VERIFY: confirm the UK/old-UK column against a current niche source before publishing — some smaller UK charts round differently below 3mm.]
mm to Yarn Weight Quick Lookup
| 2.25–3.5 mm | Fingering / sport (weights 1–2) |
|---|---|
| 3.75–4.5 mm | DK / light worsted (weight 3) |
| 5.0–5.5 mm | Worsted (weight 4) |
| 6.0–9.0 mm | Bulky (weight 5) |
| 10 mm+ | Super bulky / jumbo (weights 6–7) |
This is a starting point, not a rule — gauge and tension still vary by crocheter. For the full pairing logic and swatch guidance, see our hook size and yarn weight guide.
Printable Version
Want this chart on paper next to your project bag? We keep a dedicated printable, PDF-friendly version with a fuller size range — including steel/thread hooks — on our crochet hook size chart page. [MEDIA: a printable PDF/graphic version of the compact table above | alt: crochet hook conversion chart printable]. This page stays focused on quick digital lookups and conversions.
Frequently asked questions
How do you convert crochet hook sizes?
Use the millimeter measurement as your anchor, since it’s the one figure every brand agrees on, then cross-reference the US letter/number or UK column for the size you need. Checking the mm stamp on the hook itself is more reliable than trusting a printed letter alone.
What is a 4 mm crochet hook in US size?
A 4 mm crochet hook is a US G-6, one of the most common sizes for DK and light worsted yarn. It sits between the F-5 (3.75 mm) and the letter-less size 7 (4.5 mm).
Are UK and US crochet hook sizes the same?
No. UK and old-UK/Canadian sizing runs in the opposite direction from US letter/number sizing — the UK number gets smaller as the hook gets bigger. Always convert through the mm column rather than assume a UK number matches a US one.
What is the metric equivalent of a size H hook?
A size H hook, also written H-8, is 5.0 mm. It’s one of the most widely used sizes for worsted-weight yarn and a common recommendation for a first hook.
Where to Go Next
This page keeps to conversion only. For the fuller printable chart with steel hook sizes, see our crochet hook size chart. To understand why hook size affects gauge and how to pick a size for a project, read crochet hook sizes explained (NEW). For the mm-to-yarn pairing in more depth, see our yarn weight guide, or head back to the crochet hooks hub.