A crochet hook size chart lines up three numbering systems side by side: metric millimeters, US letters and numbers, and UK or Canadian numbers. Millimeters are the one system every hook brand agrees on, so I always check the mm stamp on the flat thumb rest first, then match it against the table below. Steel hooks, used for thread and lace work, run on a separate scale from the aluminum and plastic hooks most crocheters own, which I cover near the end of this chart.
Crochet hook size chart: mm to US and UK
Match your hook’s mm measurement against the middle column, since mm is stamped on nearly every hook regardless of brand.
| Metric (mm) | US size | UK / Canada |
|---|---|---|
| 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 |
| 5.0 mm | H-8 | 6 |
| 5.5 mm | I-9 | 5 |
| 6.0 mm | J-10 | 4 |
| 6.5 mm | no standard letter | 3 |
| 8.0 mm | L-11 | 0 |
| 9.0 mm | M/N-13 | 00 |
| 10.0 mm | N/P-15 | 000 |
Two sizes have no consistent US letter across brands. 4.5mm and 6.5mm are usually just called by their mm size, since manufacturers never agreed on a letter for either one. I always double check these two against the mm number rather than trust a letter printed on the hook.
Why there are three different hook size systems
Metric sizing measures the actual shaft diameter in millimeters, which is why it never changes between brands. US sizing grew out of an older lettered sequence that later added numbers, so G-6 and H-8 both mean something, but the letters stop making obvious sense once you pass K.
UK and Canadian sizing runs backward
This is the detail that trips up the most crocheters I hear from. UK and Canadian sizing counts down as the hook gets bigger, the opposite of US sizing, so a UK 14 is a tiny 2mm hook while a UK 000 is a huge 10mm hook. If a pattern from a UK site calls for a size 4 and you grab a US size 4, you will end up with a hook roughly 4mm too big.
Steel hooks use a different scale entirely
Steel or thread hooks, the kind used for doilies and fine lace, are not on the chart above at all. Steel sizes run in reverse of regular hooks, so a steel 00, about 3.5mm, is larger than a steel 14, about 0.75mm. My rule of thumb: if a hook is thinner than 2mm, always check whether it’s marked as a steel size before assuming it fits the chart above.
Picking the right size for your yarn
The yarn label’s suggested hook size is a starting point, not a rule. Gauge, meaning how many stitches and rows you actually get per inch, is what determines whether your project comes out the right size, and two crocheters using the same hook can still get different gauge depending on how tightly they hold the yarn. I always swatch a small square before starting anything that needs to fit.
- Fingering or lace weight: 1.5mm to 2.25mm, or a steel hook for true lace.
- DK or light worsted: 3.5mm to 4.5mm.
- Worsted weight: 5.0mm to 5.5mm, the most common range for beginner patterns.
- Bulky weight: 6.5mm to 9mm.
Frequently asked questions
What size is an H crochet hook in mm?
An H hook, also written H-8, is 5.0mm. This is one of the most common sizes for worsted weight yarn, and it’s the size I recommend most often for a first hook.
Is a bigger crochet hook a higher or lower number?
It depends on the system. In US sizing, a higher number means a bigger hook, so a J-10 is bigger than an E-4. In UK and Canadian sizing, it’s reversed, so a UK 4 is bigger than a UK 10.
Are UK and US crochet hook sizes the same?
No, they are opposite numbering systems on the same mm sizes. Always convert by mm rather than assume a UK number matches a US number, since a UK 5 and a US 5 are not the same hook at all.
What size hook comes in a beginner crochet kit?
Most beginner kits include a range from about 4.0mm to 6.5mm, roughly G through K, since that range covers worsted and bulky yarn, the easiest weights to learn with.
Find the right hook for your next project
Once you know your mm size, see our picks for the best crochet hooks in that range.