What Crochet Hook Is 5mm?

H-8. US crochet hooks pair a letter with a number rather than using a single index the way US knitting needles do — H-8 means the same 5mm hook regardless of which half of the name a specific pattern happens to print.

Why crochet hooks use a letter at all

The letter-number pairing is largely a holdover from how US hook sizing developed historically, with the letter being the older, more traditional designation and the number added later for clearer cross-reference — both refer to the identical 5mm hook, and most modern hooks print both directly on the tool itself specifically to avoid the ambiguity a letter or number alone could create.

Where 5mm sits among common hook sizes

One step down is G-6 (4mm); one step up is I-9 (5.5mm). H-8 is a frequent go-to for worsted-weight crochet, similar to how US 8 (also 5mm) is a common knitting needle size for the identical yarn weight.

Hook size and gauge aren't fixed together

A pattern's recommended hook size is a starting point, not a guarantee — crochet gauge varies by individual tension more than some knitters expect, and swatching at the recommended hook before committing to a full project is worth the extra few minutes regardless of what size the pattern's label suggests.

FAQ

Is there a metric-only crochet hook sizing system, or does every hook use the letter-number US format? Metric-only hooks are common too, especially from European manufacturers — a hook simply marked "5mm" with no letter or US number is the identical physical size as an H-8, just labeled differently.

Does H-8 always mean 5mm across every hook brand? Generally yes, since US hook lettering follows a fairly standardized convention — but always check the millimetre marking directly if precision matters, since minor variation between manufacturers isn't unheard of.

What yarn weight is a 5mm hook typically used with? Worsted weight most commonly, similar to 5mm's role on the knitting needle side — though crochet's typically looser gauge at a given hook size means a 5mm hook can also suit some bulkier yarns depending on the intended fabric density.

Does an H-8 hook work for amigurumi, or is it too large? Too large for the tight, gap-free fabric amigurumi wants — see what hook size for amigurumi for why that specific project type deliberately sizes down well below H-8 even in worsted weight.