Four countries, four ways of naming the same piece of metal. Pick a hook in whichever system your pattern, your hook, or your yarn label uses, and this shows you the other three — along with the yarn weights and ply it is normally paired with. If you only want to read the chart, the full tables are below the converter, and you can print them.
Looking for the plain reference chart instead? The crochet hook size chart lays every size out side by side on one page.
Convert a hook size
That hook in every system
—
- —US letter / number
- —Old UK / Canadian
- —Japanese
- —US steel
What hook for this yarn?
Choose a yarn weight and the usual hook range appears here.
Crochet hook conversion chart
Standard aluminum and plastic hooks. Millimeters are the controlling size; letters and numbers are conventions that drift by brand, especially above K/10.5.
| Metric (mm) | US | Old UK / Canadian | Japanese | Usual yarn weight |
|---|---|---|---|---|
| 2.25 mm | B/1 | 13 | — | 1 Super fine |
| 2.75 mm | C/2 | 12 | — | 1 Super fine |
| 3.25 mm | D/3 | 10 | — | 1 Super fine |
| 3.5 mm | E/4 | 9 | 6/0 | 1–2 Super fine to fine |
| 3.75 mm | F/5 | 9 | — | 2 Fine |
| 4.0 mm | G/6 | 8 | 7/0 | 2 Fine |
| 4.5 mm | 7 | 7 | 7.5/0 | 2–3 Fine to light |
| 5.0 mm | H/8 | 6 | 8/0 | 3 Light (DK) |
| 5.5 mm | I/9 | 5 | — | 3–4 Light to medium |
| 6.0 mm | J/10 | 4 | 10/0 | 4 Medium (worsted) |
| 6.5 mm | K/10.5 | 3 | — | 4–5 Medium to bulky |
| 8.0 mm | L/11 | 0 | 8 mm | 5 Bulky |
| 9.0 mm | M/13 | 00 | — | 5–6 Bulky to super bulky |
| 10.0 mm | N/15 | 000 | 10 mm | 6 Super bulky |
| 11.5 mm | P/16 | — | — | 6 Super bulky |
| 15.0 mm | Q | — | — | 7 Jumbo |
| 19.0 mm | S | — | — | 7 Jumbo |
Steel (thread) hook sizes
Steel hook numbers run backwards — the bigger the number, the smaller the hook. These are the Craft Yarn Council values; Boye and Bates hooks of the same number can differ by a tenth of a millimeter or more, so measure or trust the mm stamp.
| US steel size | Metric (mm) | Typical use |
|---|---|---|
| 00 | 3.5 mm | Heavy thread, fine sock yarn |
| 0 | 3.25 mm | Heavy thread |
| 1 | 2.75 mm | Size 3 crochet thread |
| 2 | 2.25 mm | Size 3–5 thread |
| 3 | 2.1 mm | Size 5 thread |
| 4 | 2.0 mm | Size 10 thread, doilies |
| 5 | 1.9 mm | Size 10 thread |
| 6 | 1.8 mm | Size 10 thread |
| 7 | 1.65 mm | Size 10–20 thread |
| 8 | 1.5 mm | Size 20 thread |
| 9 | 1.4 mm | Size 20 thread |
| 10 | 1.3 mm | Size 20–30 thread |
| 11 | 1.1 mm | Size 30 thread |
| 12 | 1.0 mm | Size 30–40 thread |
| 13 | 0.85 mm | Size 40–70 thread |
| 14 | 0.75 mm | Size 70–100 thread, tatting |
Yarn weight, ply and hook chart
Numbers and gauge ranges are the Craft Yarn Council Standard Yarn Weight System (crochet gauge is single crochet over 4 inches, except lace which is measured in double crochet). Yardage per 100 g is typical, not a standard — always read your own ball band.
| Weight | US names | UK / AU ply | Hook range | Gauge (sc / 4 in) | Yards per 100 g |
|---|---|---|---|---|---|
| 0Lace | Lace, cobweb, 10-count thread | 1–2 ply | 1.6–2.25 mm (steel 8 – B/1) | 32–42 dc | 400–800 yd |
| 1Super fine | Fingering, sock, baby | 3–4 ply | 2.25–3.5 mm (B/1 – E/4) | 21–32 | 350–450 yd |
| 2Fine | Sport, baby | 5 ply | 3.5–4.5 mm (E/4 – 7) | 16–20 | 280–350 yd |
| 3Light | DK, light worsted | 8 ply | 4.5–5.5 mm (7 – I/9) | 12–17 | 220–260 yd |
| 4Medium | Worsted, afghan, aran | 10 ply | 5.5–6.5 mm (I/9 – K/10.5) | 11–14 | 180–220 yd |
| 5Bulky | Chunky, craft, rug | 12 ply | 6.5–9 mm (K/10.5 – M/13) | 8–11 | 100–140 yd |
| 6Super bulky | Super chunky, roving | 14–16 ply | 9–15 mm (M/13 – Q) | 7–9 | 55–90 yd |
| 7Jumbo | Jumbo, roving | — | 15 mm and larger (Q and up) | 6 and fewer | 20–50 yd |
How the four systems relate
There is only one real measurement: the diameter of the hook's shaft in millimeters. Everything else is a naming convention layered on top, and the conventions disagree.
US sizes use a letter and a number together — B/1, H/8, K/10.5 — running from small to large. They are not a standard, and above K/10.5 the same letter can be a millimeter apart between brands. Old UK and Canadian sizes are numbers that run the other way: 14 is tiny, 000 is enormous. Japanese sizes end in /0 — 2/0, 6/0, 8/0 — and increase with the hook, then switch to plain millimeters above 6 mm. US steel sizes, used for crochet thread, also run backwards, from 00 (3.5 mm) down to 14 (0.75 mm), and overlap confusingly with the regular numbering.
So the conversion is not arithmetic. Every system is looked up against the millimeter value, which is why this tool converts through millimeters in both directions, and why the answer for some sizes is an em dash: not every millimeter size has a name in every country.
A worked example
Your pattern is Australian and calls for 8 ply yarn and a 4.00 mm hook, and you are standing in a US craft store holding a hook marked G/6.
- 4.00 mm in US sizing is G/6 — you have the right hook.
- In old UK numbering that is an 8; in Japanese sizing, 7/0.
- 8 ply is the Australian name for what your store calls DK or light (3) weight.
- Light weight's usual hook range is 4.5–5.5 mm, so 4.00 mm is deliberately one step tighter than the standard range — the designer wants a firmer fabric.
- Expect around 12–17 single crochets over 4 inches at the standard hook, and a little more than that on the tighter 4.00 mm.
That last line is the reason the conversion matters. If you had grabbed the 5.5 mm hook the chart calls “correct for 8 ply”, you would be about 20 % looser than the designer, and a garment would come out a size too big.
Questions people ask
What letter is a 3.5 mm crochet hook?
A US E/4. In the old UK and Canadian numbering it is a 9, and in Japanese sizing a 6/0. It suits fine (2) and light (3) weight yarns, roughly a UK 5 ply to 8 ply.
What size crochet hook for 8 ply yarn?
8 ply is the UK and Australian name for US DK or light (3) weight. It normally takes 4.5 to 5.5 mm — a US 7 through I/9 — and works up at about 12 to 17 single crochets over 4 inches. If your pattern quotes a gauge, swatch first: the ball band is a starting point, not a rule.
Are UK crochet hook sizes the same as US?
No. US uses letters, the old UK and Canadian system uses numbers that run backwards, and Japan uses its own numbering. The only measurement all three agree on is millimeters, which is why every modern hook is stamped with its mm size. When a chart and your hook disagree, trust the millimeters.
Why do two hooks marked H/8 measure differently?
US letters are a convention, not a standard, and they drift by brand and by era — most noticeably above K/10.5, where the same letter can be a whole millimeter apart. Steel hook numbers are worse: Boye and Bates have never fully agreed. Buy and substitute by millimeters instead.
What hook size should I use for worsted weight yarn?
Worsted — medium (4), 10 ply in the UK and Australia — normally takes 5.5 to 6.5 mm, a US I/9 to K/10.5. Use the smaller end for amigurumi so the stuffing cannot show through, and the larger end for blankets and anything you want to drape.