September 1, 2026
Choosing the right crochet hook is an important step in getting the look, feel and finished size you want for your project. Patterns often use a different sizing system – particularly older patterns – and hooks themselves can have different labels to refer to their size – and this even differs between brands and countries! So it can sometimes be confusing to know which one to choose.
In this tip we’ll discuss what all those different sizing systems mean and how to convert their size for what is available so it’s easier to select the right hook for your next project.
Crochet hooks may be marked using metric, UK or American (US) sizes. In some cases you may find that different brands within a country also use labels. The metric size is measured in millimetres and refers to the diameter of the hook shaft. The following is a conversion chart for common brands/countries and hook sizes.
|
Metric (mm) |
Aero/UK | Milwards/UK | Steel/US | Aluminium/ Plastic/US |
Clover/Japan |
|
0.5 mm |
7 | 14 |
14 |
||
|
0.6 mm |
7 | 6.5 |
12 |
||
|
0.75 mm |
6.5 | 5 | 13 |
10 |
|
|
0.9 mm |
6 | 4.5 | 12 |
8 |
|
|
1 mm |
5.5 | 4 | 11 |
6 |
|
|
1.1 mm |
10 |
|
|||
|
1.25 mm |
4.5 | 3 | 9 |
4 |
|
|
1.3 mm |
8 |
|
|||
|
1.5 mm |
3.5 | 2.5 | 7 |
2 |
|
|
1.75 mm |
2.5 | 2 | 6 |
0 |
|
|
1.9 mm |
5 |
|
|||
|
2 mm |
1.5 | 1 | 4 |
2/0 |
|
|
2.1 mm |
3 |
|
|||
|
2.25 mm |
2 | B |
3/0 |
||
|
2.5 mm |
0 | 2/0 | 1 |
4/0 |
|
|
2.75 mm |
0 | C |
|
||
|
3 mm |
3/0 | 3/0 | 2/0 |
5/0 |
|
|
3.25 mm |
D |
||||
|
3.5 mm |
9 | 9 | E |
6/0 |
|
|
3.75 mm |
F |
||||
|
4 mm |
8 | 8 | G |
7/0 |
|
|
4.5 mm |
7 | 7 | 7 |
7.5/0 |
|
|
5 mm |
6 | 6 | H |
8/0 |
|
|
5.5 mm |
5 | 5 | I |
9/0 |
|
|
6 mm |
4 | 4 | J |
10/0 |
|
|
6.5 mm |
K |
||||
|
7 mm |
2 | 2 |
|
||
|
8 mm |
L |
||||
|
9 mm |
M |
||||
|
10 mm |
P |
||||
| 15 mm | Q |
|
Note: – Susan Bates often has a different size labelling again.
My tip: wherever possible, refer to the millimetre measurement, as it has become the most widely used standard among manufacturers and pattern writers.
Your yarn label is also a great place to start. Most yarn balls include a recommended crochet hook size, giving you a useful guide based on the thickness and characteristics of the yarn. Keep in mind that this is only a recommendation—your pattern may specify a different size depending on the desired result, and of course your tension my differ.
The pattern you are following will usually recommend a hook size, but again, this is a starting point rather than a rule. Your individual tension, the yarn you are using and the way you crochet can all affect the finished fabric.
For garments, blankets and other projects where the finished size matters, always check your tension (gauge) swatch before starting. The right hook size is the one that helps you achieve the tension specified in the pattern. Refer to our tip on gauge swatches here to read more about preparing and using a gauge swatch.
Choosing the right hook size for your project doesn’t have to be complicated. Start with the pattern, refer to the conversion chart if necessary, and prepare a gauge swatch. You will learn your style over time, and choosing the right size hook will become second nature in no time!
Read our tip on preparing and using gauge swatches here
