Converter
Crochet hook sizes
Type a millimetre figure or pick a US or UK size. You get the equivalent in the other two systems, plus the yarn weights that hook is normally used with.
Hook size chart
US and UK sizes are not standardised between manufacturers. Buy by millimetre.
| Metric | US | UK | Typical yarn weight |
|---|---|---|---|
| 1.4 mm | steel 8 | — | 0 Lace |
| 1.5 mm | steel 7 | — | 0 Lace |
| 1.75 mm | steel 5 | — | 0 Lace |
| 2 mm | steel 4 | 14 | 0 Lace |
| 2.25 mm | B/1 | 13 | 0 Lace |
| 2.5 mm | C/2 | 12 | 1 Super fine |
| 2.75 mm | C/2 | 11 | 1 Super fine |
| 3 mm | D/3 | 11 | 1 Super fine |
| 3.25 mm | D/3 | 10 | 1 Super fine |
| 3.5 mm | E/4 | 9 | 1 Super fine |
| 3.75 mm | F/5 | 9 | 2 Fine |
| 4 mm | G/6 | 8 | 2 Fine |
| 4.5 mm | 7 | 7 | 2 Fine |
| 5 mm | H/8 | 6 | 3 Light |
| 5.5 mm | I/9 | 5 | 3 Light |
| 6 mm | J/10 | 4 | 4 Medium |
| 6.5 mm | K/10.5 | 3 | 4 Medium |
| 7 mm | K/10.5 | 2 | 5 Bulky |
| 8 mm | L/11 | 0 | 5 Bulky |
| 9 mm | M/13 | 00 | 5 Bulky |
| 10 mm | N/15 | 000 | 6 Super bulky |
| 12 mm | P/16 | — | 6 Super bulky |
| 15 mm | Q | — | 6 Super bulky |
| 16 mm | S | — | 7 Jumbo |
| 19 mm | T | — | 7 Jumbo |
| 25 mm | U | — | 7 Jumbo |
How to read a hook size
A crochet hook is sized by the diameter of its shaft — the straight section between the throat and the thumb rest, not the hook itself. That is why two hooks marked "H/8" can differ: one brand's H is 5.0 mm, another's is 5.5 mm. The millimetre figure is the only one that means the same thing everywhere.
US sizing uses letters and numbers together (B/1, H/8, K/10.5) and skips around; UK sizing uses the old needle-number system where a larger number is a smaller hook. If a pattern gives you only a letter, convert it to millimetres before you shop.
Which hook for which yarn
The label on a ball of yarn usually prints a recommended hook range. As a starting point: lace and thread use 1.4–2.25 mm, fingering 2.25–3.5 mm, sport 3.5–4.5 mm, DK 4.5–5.5 mm, worsted 5.5–6.5 mm, bulky 6.5–9 mm and super bulky 9–15 mm.
Those are starting points, not rules. Gauge is what decides the finished size, and the gauge converter will tell you what to change if your swatch does not match the pattern.
How to measure a hook you already own
Hold the shaft — the straight part between the throat and the handle — against a ruler with a millimetre scale, or push it through the holes on a plastic needle gauge. Do not measure the hook itself or the widest part of the thumb rest; both will give you a size that is too large. If the shaft sits between two sizes, round down: a hook that is slightly small produces a tighter, more predictable fabric than one that is slightly large.
This matters more than it sounds. Hooks lose their markings, inherited sets get mixed, and a "4 mm" from one brand measures 3.9 mm while another measures 4.2 mm. The measurement is the only fact in the room.
Choosing a hook for the project
The label recommendation is a starting point for the yarn, not for the pattern. Project type moves it:
- Amigurumi and toys: one to two sizes below the label, so the fabric is dense enough to hold stuffing without gaps.
- Lace and shawls: one to two sizes above, to open the stitch pattern and improve drape.
- Garments: the size that hits the pattern's gauge, whatever the label says. Gauge is the only number that decides fit.
- Blankets and homeware: the label size, worked loosely; drape matters less than speed.
- Tunisian crochet: one to two sizes above the equivalent regular hook, because the return pass tightens the fabric.
Questions people ask
What are the crochet hook sizes?
Metric sizes run from 1.4 mm to 25 mm. US sizes use letters and numbers (B/1 through U) and UK sizes use old numbers (14 down to 000). Metric is the only figure that is consistent between brands.
What letter size is a 4.00 mm crochet hook?
G/6. A 4.5 mm hook is a US 7, and a 5.0 mm hook is H/8.
How do I tell what size crochet hook I used?
Measure the shaft — the part just below the thumb rest — with a caliper or against a printed gauge. The letter on the handle is not reliable across brands.
Can I use a knitting needle size chart for crochet hooks?
No. They share the millimetre scale but not the numbering — a US 7 knitting needle is 4.5 mm, while a US 7 crochet hook is also 4.5 mm but the letters around it do not line up. Convert both to millimetres and compare those.
Does hook size change the stitch size?
Yes. Going up one hook size loosens the fabric and increases the finished size; going down tightens it. For amigurumi, one size down from the label is common.