Crochet Hook Size Converter

The Crochet Hook Size Converter translates a crochet hook size between the three systems used around the world — US letter/number designations, UK/Canada numbering, and the metric (mm) scale — so you can follow any pattern no matter where it was written. Enter a size in the system you know and the tool shows every equivalent at once, along with the recommended yarn weight and the next sizes up and down.

How Crochet Hook Sizing Works

Crochet hooks are sized by the diameter of the shaft in millimetres, but each region labels that diameter differently:

• Metric (mm): The shaft diameter, e.g. 4.0 mm or 5.5 mm. This is the most precise and least ambiguous system, used internationally and increasingly on US patterns too.
• US: A letter paired with a number, e.g. G/6 or H/8. Larger letters mean larger hooks.
• UK / Canada: A single number that runs in the opposite direction — a larger number means a smaller hook (UK 14 ≈ 2 mm, UK 2 ≈ 7 mm).

Crochet Hook Size Conversion Chart

This is the standard yarn-hook conversion chart this tool uses. Steel (thread) hooks have their own chart further down.

Common Crochet Hook Conversions

• 3.5 mm = US E/4 = UK 9 — light DK projects
• 4 mm = US G/6 = UK 8 — the classic amigurumi and worsted hook
• 5 mm = US H/8 = UK 6 — the most-used all-rounder
• 5.5 mm = US I/9 = UK 5 — blankets and garments in aran
• 6 mm = US J/10 = UK 4 — chunky scarves and hats
• 8 mm = US L/11 = UK 0 — bulky throws

Steel (Thread / Lace) Crochet Hooks

Steel hooks are used for fine thread crochet, doilies, and lace. They use a separate scale — note that the same numbers mean far smaller hooks than yarn hooks (US steel 1 is 2.75 mm, not the 2.25 mm of a yarn B/1).

Why Gauge Still Matters After Converting

A conversion chart gets you the right hook diameter, but the finished size of your project depends on your personal tension. Two crocheters using the same 5 mm hook and the same yarn can produce different gauge. Always crochet a gauge swatch and compare it to the pattern; if your swatch is too tight, go up a hook size, and if it is too loose, go down. The "one size up / one size down" suggestions in the results make this easy.

How to Use This Calculator

1. Choose the system you know: Metric (mm), US, or UK/Canada.
2. Enter your hook size: Type the value (e.g. 5 mm, H/8, or 6), or click a quick-pick size chip.
3. Click Convert: The tool finds the matching standard hook.
4. Read every equivalent: See all three systems, the recommended yarn weight, the position on the visual scale, and the neighbouring sizes for gauge adjustments.

Frequently Asked Questions

How do I convert a crochet hook to US size?

Find your hook on the metric (mm) scale, then read across to the US column. For example, a 5 mm hook is a US H/8, a 4 mm hook is a US G/6, and a 6 mm hook is a US J/10. This converter does that lookup for you and shows the US, UK/Canada and metric values together.

Why do UK crochet hook numbers go down as the hook gets bigger?

The UK/Canada system numbers hooks in the opposite direction to the US letters: a larger UK number means a smaller hook. A UK 14 is only 2 mm, while a UK 2 is 7 mm. Because the two systems run opposite ways, it is safest to convert through the metric millimetre size, which is unambiguous.

What size is an H crochet hook?

A US H hook, written H/8, is 5 mm and corresponds to UK/Canada size 6. It is one of the most common hooks and is typically used with worsted or aran weight yarn.

Are steel crochet hooks measured differently?

Yes. Steel hooks are used for fine thread and lace crochet and use a separate numbering scale where the millimetre size is much smaller, even though some numbers overlap with yarn hooks. A US steel 1 is 2.75 mm, not the 2.25 mm of a yarn-hook B/1. This tool keeps the two scales in separate tables.

What yarn weight goes with which hook size?

As a guide: lace and fingering yarn use 2.25–3.5 mm hooks, DK uses 3.5–4.5 mm, worsted/aran uses 5–6.5 mm, chunky/bulky uses 6.5–9 mm, and super bulky or jumbo yarn uses 9–19 mm or larger. Always check your pattern and crochet a gauge swatch, because tension varies between crocheters.

My pattern hook isn't an exact mm size. What do I do?

Enter the closest millimetre value and the converter will snap to the nearest standard hook and tell you it is approximate. It also shows the next size up and down so you can adjust if your gauge swatch comes out too tight or too loose.

Additional Resources

• Crochet Hook - Wikipedia
• Crochet Hook Sizes - Craft Yarn Council