Metric
— mm
US — · UK — · JP —
Yarn weight: —
| Metric (mm) | US | UK | Japan | Typical yarn |
|---|
How the math works
Hook sizing is a lookup, not a formula. Metric mm is the only true measurement — US, UK and Japanese systems each use letters or numbers that map to a hook diameter. The chart below uses Craft Yarn Council standards.
UK numbers go DOWN as the hook gets bigger (opposite of metric). Always check gauge on your project — different manufacturers vary by ±0.1 mm.