Crochet Hook Size Converter
Convert hook sizes between US letter, metric (mm), and UK/Canadian systems.
Quick Converter
Standard Hook Sizes — Full Reference Table
| US Size | Metric (mm) | UK / Canadian |
|---|
Steel Crochet Hook Sizes (Thread/Lace)
| Steel Size (US) | Metric (mm) | Notes |
|---|
How to Use This Converter
- Use the Quick Converter at the top — select your size system and the hook size, and see all equivalents instantly.
- Use the search box above each table to filter rows as you type. Type a US size like "G/6", a metric size like "4", or a UK number like "8".
- Standard hooks (B/1 through S/19) are for regular yarn. Steel hooks (sizes 00–14) are for fine thread and lace work.
Understanding Hook Size Systems
- US: Uses a letter/number combo (B/1, C/2…). Larger letters = larger hooks.
- Metric (mm): The most precise system — measures the actual shaft diameter. Used internationally.
- UK/Canadian: An older numbering system where higher numbers mean smaller hooks — the opposite of the US system. Less common today.
- When patterns list only one system, use the mm measurement to match accurately.
About this Crochet Hook Size Converter
Crochet hooks are sized using three different systems — US letter/number sizes, UK sizes, and metric millimeter sizes — and the US and UK systems don't correspond in an intuitive order, which makes converting between them essential when working from patterns sourced internationally.
Metric size is the most reliable reference
Because letter and number sizing conventions vary and have changed over time, the millimeter diameter is the most unambiguous way to confirm you're using the correct hook, regardless of which labeling system a specific pattern or hook manufacturer uses.