Crochet Hook Size Conversion Chart – AU, US & UK (mm)
Use this crochet hook size conversion chart to compare US hook letters and numbers with metric millimetres (mm) and older UK hook sizes. In Australia, most modern crochet hooks and patterns use millimetres, making metric measurements the easiest starting point when following overseas patterns.
A 5 mm crochet hook is commonly labelled US H-8 and old UK size 6. A 4 mm hook is typically US G-6 or old UK size 8. Australian hook sizes are generally given in mm. Older UK numbers are not the same as modern metric sizes; US labels can vary by manufacturer.
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Crochet Hook Size Conversion Chart
The Australia (AU) / Metric (mm) column is the usual modern Australian size. US labels follow the Craft Yarn Council size reference where listed. The older UK numbers are approximate historical equivalents, not a current official standard; different vintage charts may disagree. A dash means no dependable equivalent is shown.
| Australia (AU) / Metric (mm) | US hook size | Old UK hook size |
|---|---|---|
| 2.00 mm | — | 14 |
| 2.25 mm | B-1 | 13 |
| 2.50 mm | — | — |
| 2.75 mm | C-2 | 12 (varies) |
| 3.00 mm | — | 11 |
| 3.25 mm | D-3 | 10 |
| 3.50 mm | E-4 | 9 (varies) |
| 3.75 mm | F-5 | — |
| 4.00 mm | G-6 | 8 |
| 4.25 mm | G (varies) | — |
| 4.50 mm | 7 | 7 |
| 5.00 mm | H-8 | 6 |
| 5.50 mm | I-9 | 5 |
| 6.00 mm | J-10 | 4 |
| 6.50 mm | K-10½ | 3 |
| 7.00 mm | — | 2 |
| 8.00 mm | L-11 | 0 |
| 9.00 mm | M/N-13 | 00 |
| 10.00 mm | N/P-15 | 000 |
| 11.50 mm | P-16 | — |
| 12.00 mm | — | — |
| 15.00 mm | P/Q (varies) | — |
Important: These are guides, not guaranteed manufacturer-to-manufacturer matches. In particular, avoid using old UK equivalents as exact measurements. For example, US G hooks may be labelled 4 mm or 4.25 mm. Always prefer the mm marking on your hook or yarn pattern.
How Crochet Hook Sizes Work in Australia, the US and the UK
Australian (AU) sizes: millimetres
In Australia, modern crochet hook sizes are normally labelled by the hook's diameter in millimetres, such as 3.5 mm, 4 mm or 5 mm. This is the clearest measurement to compare when buying hooks.
US sizes: letters and numbers
US hooks often use combinations such as G-6, H-8 and J-10. These labels are convenient but not perfectly consistent across brands, so check the printed mm value too.
Old UK sizes: historic numbers
Older British crochet patterns sometimes list numbered hooks, such as 8, 6 or 4. These old UK numbers generally decrease as the hook gets larger. Most contemporary UK patterns use metric sizing, so only use the old UK column when interpreting a genuinely older pattern.
How to Choose the Right Crochet Hook
- Read the pattern: Look for a hook diameter in mm. If only a US letter or older UK size is supplied, use the chart as a starting point.
- Check the yarn label: It often provides a suggested hook range, but this is a recommendation rather than a compulsory size.
- Make a gauge swatch: Crochet a small sample in the stated stitch and measure it against the pattern's gauge, particularly for garments.
- Adjust if needed: If you have more stitches per 10 cm than required, try a larger hook. If you have fewer, try a smaller one.
Hook Size, Yarn Weight and Finished Fabric
A smaller hook usually creates denser stitches; a larger hook usually produces a looser, more open fabric with the same yarn. For toys such as amigurumi, designers often use a smaller hook to reduce gaps in the stuffing. For shawls and lace, a larger hook can create a more open look.
Do not assume a specific hook size is correct for every yarn weight. Yarn fibre, twist, stitch choice, individual tension and the intended fabric all matter.
Regular Crochet Hooks vs Steel Crochet Hooks
Small steel hooks used for fine thread and lace can have their own numbering system. For many steel hook ranges, higher numbers represent smaller hooks. Do not compare a steel hook number directly with a regular US hook number. Check the diameter in mm instead.
Common Mistakes When Converting Crochet Hooks
- Confusing an old UK numbered hook with a modern US numbered hook.
- Assuming every US letter has one exact metric equivalent across all brands.
- Using knitting needle size conversions for crochet hooks.
- Skipping a gauge swatch when fit or finished dimensions matter.
- Confusing US and UK stitch terminology, which is a separate issue from hook sizing.
Crochet Hook Size FAQs
What is a 4 mm crochet hook in US sizing?
A 4 mm crochet hook is commonly labelled US G-6. Some brands label a G hook 4.25 mm, so check the stated metric diameter.
What is a US H-8 crochet hook in Australia?
A US H-8 is commonly a 5 mm crochet hook in Australia.
Are Australian crochet hook sizes the same as metric sizes?
Yes. In Australia, crochet hooks are generally sold by diameter in millimetres, such as 3.5 mm, 4 mm or 5 mm. The AU and metric measurements in the chart are the same, so a separate AU column would duplicate the values.
Are Australian and UK crochet hook sizes the same?
Contemporary Australian and British patterns generally use millimetres, so a 5 mm hook means the same diameter in both countries. Older UK numbered hooks use a different historical system.
What is old UK size 6 in millimetres?
Old UK size 6 is commonly listed as approximately 5 mm. Check the original pattern and your hook's metric marking where possible.
Do US and UK crochet patterns use the same stitches?
Not always. For example, a US single crochet is called a UK double crochet. Confirm whether the pattern uses US or UK stitch terms before starting.
Can I substitute a different hook size?
Often, but the finished dimensions and fabric may change. Test with a gauge swatch and follow the pattern's finished-measurement requirements.
Explore More Fosmore Guides
Explore additional practical conversion resources in the Fosmore Size Charts Hub or browse the Size Guides Hub. As more crochet, knitting and yarn guides are published, they can be linked from this page.
Reference and Sizing Notes
This guide uses modern metric and US hook conventions described by the Craft Yarn Council, with historical UK conversions treated as approximate. For official background, see the Craft Yarn Council hook standards. This reference opens in a new tab.
Disclaimer
Crochet hook conversions are approximate and may vary by manufacturer, especially for older UK systems and US letter sizes. Check the millimetre marking, yarn label and pattern gauge before starting. This guide is for general educational use and does not guarantee a particular project fit or result.