Crochet Hook Size Converter

In short Crochet hooks are labelled three ways and, as with knitting needles, only the millimetre is an actual measurement. The US system uses a letter and a number together — B-1, G-6, H-8 — and the UK uses a numbered scale that runs backwards, getting smaller as the hook gets bigger. An H-8 is 5 mm and a G-6 is 4 mm, and those two are the hooks most patterns start from. The important caveat is specific to crochet and worth knowing before you order anything: above about K, the US letters genuinely disagree between manufacturers. A 9 mm hook is sold as M by some and N by others, and a 10 mm as N or P. That is not a gap in this table, it is a real inconsistency in the labelling, and it is the reason experienced crocheters quote hooks in millimetres and ignore the letter. Two further points. The letter and the number in a US size are not two systems — they are one label with two parts, so "G-6" is a single size and not a range. And hook size affects crochet gauge more sharply than needle size affects knitting gauge, because a crochet stitch wraps the hook rather than sitting on it, so half a millimetre changes the fabric noticeably. If your gauge is off, changing hook size is the correct fix, exactly as with knitting.