Hook sizing is needlessly confusing, and for one reason: there are three numbering systems in circulation and they do not agree. A pattern might call for an H, a 5 mm, or a 4 — and depending on which system it means, those are not necessarily the same hook.
Ignore the letters. The millimetre measurement is the only reliable number, because it is a physical measurement of the shaft rather than a label. If you are starting out, buy a 5 mm hook and nothing else until you know what you are missing.
The systems
Metric (mm) — the diameter of the hook's shaft. This is the actual measurement and the one every modern pattern should give. Use this.
US letters and numbers — B, C, D, E, F, G, H and so on. A convention, not a measurement. It has varied between manufacturers over the years, which is why an old pattern's "H" and your "H" may differ slightly.
UK numbers — an older system that runs backwards: the bigger the number, the smaller the hook. Still found in vintage patterns and a reliable source of ruined projects.
| Metric | US | Typical use |
|---|---|---|
| 2.25 mm | B-1 | Fine yarn, amigurumi detail |
| 2.75 mm | C-2 | Fine yarn |
| 3.5 mm | E-4 | Sport weight |
| 4 mm | G-6 | DK weight |
| 5 mm | H-8 | Worsted / aran — the usual starting point |
| 5.5 mm | I-9 | Worsted, looser |
| 6 mm | J-10 | Chunky |
| 8 mm | L-11 | Chunky and super chunky |
| 10 mm | N/P-15 | Super chunky, blankets |
Steel hooks for thread work use their own scale, and it also runs backwards — a 14 steel hook is much finer than a 6.
Matching hook to yarn
Yarn labels carry a recommended hook size, and it is a genuinely good starting point. But it is a suggestion, not a rule, and two things change it.
What you are making. The same yarn wants a different hook depending on the job:
- A blanket or a scarf — the recommended size, or one larger. You want drape and softness.
- A bag — one or two sizes smaller. You want dense, firm fabric that holds its shape and does not let contents poke through.
- Amigurumi (stuffed toys) — noticeably smaller than recommended. The fabric must be tight enough that stuffing does not show through the stitches, which is why toy patterns often specify a 3 mm hook for yarn labelled 5 mm.
Your own tension. Some people crochet tightly and some loosely, and it is consistent for each person. If your work always comes out smaller than the pattern says, you crochet tightly and should go up a size. The reverse if it comes out large.
Patterns state a hook size and a gauge — how many stitches should fit in ten centimetres. The gauge is the real requirement. If your gauge does not match with the stated hook, change the hook until it does. This is why two people can follow the same pattern with the same hook and produce garments two sizes apart.
Materials, and whether it matters
For the finished fabric, barely. For your hands over three hours, considerably.
Aluminium — slick and fast, yarn slides easily. The usual default, and good for beginners because it does not fight you.
Bamboo and wood — warmer to hold and grippier, which some people like for slippery yarns and others find slows them down.
Plastic — cheap and light. Large sizes are often plastic because metal would be heavy.
Ergonomic handles — a soft grip on a metal shaft. Genuinely worth it if you crochet for long stretches or have any joint pain, and unnecessary otherwise.
There is also a difference in the head shape: inline hooks (a flat, straight throat) and tapered hooks. People develop strong preferences, but neither is better. If your stitches keep splitting, try the other kind.
What to actually buy
Starting out: one 5 mm hook. That is not a joke — a single hook and one ball of yarn is the correct beginner purchase, and it costs very little.
After a few projects: add 4 mm and 6 mm. Those three cover the majority of ordinary patterns.
Once you know what you make: buy for that. Amigurumi people need small hooks; blanket people need large ones. Buying a forty-piece set first means owning thirty-five hooks you never touch, usually in a quality that would not have been your choice.
The one accessory genuinely worth having early is a stitch marker — and a safety pin or a scrap of contrasting yarn does the job perfectly.
See also: crochet for absolute beginners.
Frequently asked questions
What size hook should a beginner buy?
5 mm, also labelled H-8 in US sizing. It is big enough to see what you are doing and suits the worsted or aran weight yarn most beginners start with.
Why do hooks have both letters and numbers?
The letters are a US convention and the numbers are millimetres. The millimetre figure is the real measurement; the letter is a label that has varied between manufacturers. Always go by the millimetres.
What happens if I use the wrong size hook?
A hook too small gives stiff, dense fabric that is hard to work. A hook too large gives loose, floppy fabric with visible gaps. Neither is wrong for every project, but both will make a garment come out the wrong size.
Does the hook material matter?
For comfort, yes. Aluminium is slick and fast, bamboo and wood grip the yarn more, and plastic is light and cheap. For beginners a slick hook is usually easier, and a soft handle helps if your hand tires.
What are steel hooks for?
Very fine thread work — doilies, lace and fine edging. Confusingly, steel hook numbering runs backwards: a higher number means a smaller hook. Beginners do not need them.
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