StitchCalcsKnitting needle and crochet hook size converter
Convert between metric (mm) and US knitting needle and crochet hook sizes, with the full size charts for both.
Why sizes don't always match
US needle numbers and hook letters were never fully standardised, so different brands sometimes give the same US size to slightly different diameters. That's why the charts below list a few US sizes twice. The millimeter size is an actual measurement of the diameter, so it's the one to trust. The Craft Yarn Council, whose standards these charts follow, gives the same advice.
UK and Canadian needles from before metric sizing used a different numbering, where bigger numbers meant thinner needles. If an old pattern gives a size like "UK 8", look up a vintage conversion chart, or go by the gauge the pattern asks for.
Knitting needle sizes
| Metric | US |
|---|
Crochet hook sizes
| Metric | US |
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A dash means the chart lists no US equivalent for that metric size. Source: Craft Yarn Council hook and needle standards, checked September 2026. Steel crochet hooks for thread use a separate numbering and are not included.