Crochet hook sizes in mm range from about 0.5mm steel hooks used for fine thread work up to 15mm or larger jumbo hooks used for extreme bulky yarn. I always think in mm first, since it’s the one measurement that’s consistent across every brand, unlike US letters or UK numbers.
The mm range at a glance
Steel and thread hooks run from about 0.5mm to 1.75mm, standard yarn hooks run from 2.0mm to about 10mm, and jumbo hooks go from 11.5mm upward for arm-crochet style projects. Most everyday crochet, garments, blankets, and amigurumi, falls in the 3.5mm to 6.5mm range.
- Steel/thread range: 0.5mm to 1.75mm, for lace and doilies.
- Standard range: 2.0mm to 10mm, for yarn weights from lace through super bulky.
- Jumbo range: 11.5mm and up, for extreme bulky or multi-strand projects.
Why I check mm before US or UK sizing
US letters and UK numbers both have gaps and inconsistencies, especially in the middle of the range where several sizes have no standard letter at all. I’ve been caught out before trusting a printed letter that turned out to vary between two brands I owned, so now I check mm on every hook by default.
Frequently asked questions
What is the smallest crochet hook size in mm?
Steel thread hooks go down to around 0.5mm, though most crocheters working with yarn rather than thread will never go below 2.0mm.
What is the largest crochet hook size in mm?
Jumbo hooks go up to 15mm or larger, used mainly for extreme bulky yarn or arm-crochet style projects.
See the full mm to US and UK chart
Get exact US letter and UK number equivalents for every mm size.