US Crochet Hook Size To mm Converter
Find the metric millimetre size for a US crochet hook label, then check whether the yarn, pattern gauge and hook style still match your project.
Choose A US Crochet Hook
Metric Hook Result
Recommended metric lookup for the selected US label.
Quick Conversions For Common Crochet Hooks
G/6
G/6 is commonly listed as 4.00 mm. It is often used with DK or light worsted yarn where a neat but not stiff fabric is wanted.
H/8
H/8 is commonly listed as 5.00 mm. Many beginner patterns use it with worsted or aran-style yarn because the stitches are easy to see.
I/9
I/9 is commonly listed as 5.50 mm. It can help loosen fabric for blankets, scarves or garments when the pattern gauge is not tight.
J/10
J/10 is commonly listed as 6.00 mm. It is a frequent choice for chunkier yarns, quick blankets and relaxed accessories.
Conversion Method For US Hook Labels
US crochet hook conversion is a lookup, not a mathematical formula. The letter or number printed on the hook is a naming system. The metric millimetre value describes the hook shaft diameter more directly. When a pattern says US H/8, the useful metric answer is 5.00 mm, but the exact grip, throat, head shape and brand finish can still affect gauge.
For most yarn crochet, the millimetre size is the better number to keep in a project note. If you buy hooks in the UK or Europe, packaging usually leads with mm. If you read a US pattern, the label may lead with the letter and number. This converter links the two so you can buy the nearest tool, but gauge swatching is still needed for fitted garments, toys, motifs that must join cleanly, or any project where final size matters.
US Crochet Hook To mm Table
| US label | Metric size | Typical use note |
|---|---|---|
| B/1 | 2.25 mm | Fine cotton, lace-weight yarn or small details. |
| C/2 | 2.75 mm | Fine yarn, small motifs and firm fabric. |
| D/3 | 3.25 mm | Light yarn and tight stitch work. |
| E/4 | 3.50 mm | Sport or light DK yarn in many patterns. |
| F/5 | 3.75 mm | DK yarn, neat blankets and garments. |
| G/6 | 4.00 mm | DK or light worsted yarn. |
| 7 | 4.50 mm | Often sits between G/6 and H/8. |
| H/8 | 5.00 mm | Worsted, aran and many beginner patterns. |
| I/9 | 5.50 mm | Open fabric or slightly heavier yarn. |
| J/10 | 6.00 mm | Chunky yarn and quick blankets. |
| K/10.5 | 6.50 mm | Bulky yarn and relaxed stitch fabric. |
| L/11 | 8.00 mm | Super bulky yarn or loose texture. |
| M/13 | 9.00 mm | Large stitches and soft heavy yarn. |
| N/15 | 10.00 mm | Very bulky projects. |
| P/16 | 11.50 mm | Extra bulky yarn and oversized fabric. |
| Q | 15.00 mm | Arm-style chunky yarn effects with a hook. |
| S | 19.00 mm | Very large novelty yarn or cord. |
Using The Result In A Pattern
If a pattern gives both US and metric sizes, follow the metric size where possible because it is the more precise tool measurement. If the pattern gives only a US hook label, use the conversion as a starting hook, then make a gauge square. Count stitches and rows across the measurement named by the pattern. If your swatch has too many stitches in the measured width, your stitches are too small and you may need a larger hook. If it has too few stitches, try a smaller hook.
Amigurumi and stuffed toys often need a tighter fabric so filling does not show through. A maker may intentionally use a smaller hook than the yarn band suggests. Lace, shawls and draped garments may use a larger hook for openness. That is why the converter result should sit beside the pattern gauge rather than replace it. Also check whether the pattern mentions inline hooks, tapered hooks, ergonomic handles or steel hooks, because the hook shape can change how stitches slide and sit.
Steel Crochet Hook Warning
Very small steel crochet hooks, often used for thread crochet, can have their own numbering conventions. Some steel hook numbering systems run in the opposite direction from larger yarn hooks, where a bigger number may mean a smaller hook. This converter is aimed at common yarn crochet hook labels such as G/6, H/8 and J/10. If your hook is a fine steel hook for thread, check the manufacturer’s metric marking or a steel-hook-specific chart before ordering.
Reading Yarn Bands With US Patterns
A yarn band may suggest a metric hook range, while a US pattern may list one hook label. Treat both as starting information. If the yarn band says 4.00 to 5.00 mm and the pattern says H/8, the 5.00 mm result sits at the larger end of that range. That may be perfect for drape, but it may be too loose for a stuffed toy or bag. Keep the converted size, yarn band range and your gauge result together in the project notes so a second skein or later repair is easier to match.
FAQ
What is a US H/8 crochet hook in mm?
A US H/8 crochet hook is commonly listed as 5.00 mm.
Is a US G/6 hook 4 mm or 4.25 mm?
Most modern yarn charts list G/6 as 4.00 mm. Some older or brand-specific charts may differ, so use the mm marking on the hook when it is printed.
Why does my gauge differ with the right hook size?
Tension, yarn twist, fibre, hook shape and hand position can all change gauge. The converted hook size is only the starting tool.
Can I use this chart for UK crochet hooks?
Use the metric mm result for UK buying. Older UK hook numbers are separate and can be checked with a UK-to-mm chart.
What if my pattern says size 7?
US size 7 is commonly 4.50 mm. It sits between G/6 and H/8, so do not treat it as the same as either neighbour.
Are steel hooks included?
No. Fine steel thread hooks can use a different numbering pattern. Check the printed mm size or a steel hook chart.
Sources
- Craft Yarn Council. (n.d.). Standards and Guidelines for Crochet and Knitting. Craft Yarn Council. https://www.craftyarncouncil.com/standards
- British Standards Institution. (n.d.). Textiles and Craft Measurement Standards. BSI. https://www.bsigroup.com/