Crochet Hook Sizes: Conversion Chart
The full US, metric, and UK hook size chart in one table, plus which hook to grab for the yarn weight you're holding.
Crochet hooks are sized by shaft diameter in millimeters, and mm is the only fully reliable system. A 5.0mm hook is US H-8 and old UK/Canada size 6. US letters and old UK numbers both have gaps and disagreements at the small and large ends, so when a pattern gives a metric size, trust that first.
Two hooks stamped with the same US letter can still measure differently, because the mm-to-letter mapping was never enforced by one standards body the way yarn weights are. The metric size stamped on the shaft is the one number that stays constant across brands and countries.
The full US, metric, and UK hook size chart
| 2.25mm | US B-1 · UK 13 |
| 2.75mm | US C-2 · UK 11 |
| 3.25mm | US D-3 · UK 10 |
| 3.5mm | US E-4 · UK 9 |
| 3.75mm | US F-5 · UK n/a |
| 4.0mm | US G-6 · UK 8 |
| 4.5mm | US 7 · UK 7 |
| 5.0mm | US H-8 · UK 6 |
| 5.5mm | US I-9 · UK 5 |
| 6.0mm | US J-10 · UK 4 |
| 6.5mm | US K-10½ · UK 3 |
| 8.0mm | US L-11 · UK 0 |
| 9.0mm | US M/N-13 · UK n/a |
| 10.0mm | US N/P-15 · UK n/a |
| 12.0mm | No agreed US letter · UK n/a |
| 15.0–16.0mm | US Q · UK n/a |
| 19.0mm | US S · UK n/a |
B-1 through L-11 is the range covered by nearly every hook set and pattern, and every major source agrees on it exactly. Above 9mm, treat the US number as primary and the letter as a rough label. See the callout below for why.
Which hook size for which yarn weight
The Craft Yarn Council publishes the standard that yarn manufacturers print on ball bands, and it maps each weight to a hook range. Use it to go straight from the yarn in your hand to the hook you should grab.
| Lace (0) | 2.25mm and steel hooks, or US B-1 |
| Super Fine (1) · sock, fingering, baby | 2.25–3.5mm · US B-1 to E-4 |
| Fine (2) · sport, baby | 3.5–4.5mm · US E-4 to 7 |
| Light (3) · DK, light worsted | 4.5–5.5mm · US 7 to I-9 |
| Medium (4) · worsted, afghan, aran | 5.5–6.5mm · US I-9 to K-10½ |
| Bulky (5) · chunky, craft, rug | 6.5–9mm · US K-10½ to M-13 |
| Super Bulky (6) · roving | 9–15mm · US M-13 to Q |
| Jumbo (7) · roving | 15mm and up · US Q and larger |
Why the letters stop making sense above 9mm
Manufacturers never fully agreed on letters for the largest hooks. A 9mm hook is sold as M-13 by some brands and N-13 by others. A 10mm hook shows up as N-15 or P-15. This isn't a mistake in any single chart, it's a real disagreement between brands. The US number is more consistent than the letter at this end, so if a pattern gives you a size like "P/Q," check the mm on the hook itself before you buy.
What about UK sizing?
UK and Canadian hook sizes are a legacy system and run in reverse of US sizing: a bigger number means a smaller hook. A UK 13 is tiny (2.25mm) and a UK 0 is large (8mm). This system predates metric standardization, which is also why a couple of old UK sizes overlap at the small end. Modern UK pattern writers have mostly moved to metric mm, so you'll only run into UK numbers when reading a vintage British or Canadian pattern.
Do I need steel hooks?
Steel hooks are a separate size system for thread and lace crochet, running roughly 0.6mm to 2.75mm, sized 00 (largest) to 14 (smallest), reverse of standard hook numbering. Sizing varies more between brands here than on regular hooks, so check the mm on the hook itself. They're worth owning only if you're working with crochet thread rather than yarn. If you're crocheting with yarn, the standard hooks in the chart above cover you.
Why do two hooks marked the same letter feel like different sizes?
US letter sizing was never enforced by a single standards body the way metric sizing is. Brands vary slightly, especially above 9mm. Always trust the mm stamped on the hook over the letter.
What's the difference between a UK and US crochet hook size?
They're reverse-numbered. UK sizing gets smaller as the number goes up, US sizing (where it uses numbers) gets larger. Match by millimeter, not by comparing the numbers directly.
Do I need steel hooks for regular yarn crochet?
No. Steel hooks are sized for thread and lace work. Yarn projects use the standard aluminum, wood, or ergonomic hooks in the main chart.
What size hook comes with most beginner kits?
Usually 4.0–5.0mm, US G to H, matched to worsted-weight yarn, which is the most common beginner yarn.