US Crochet Hook Sizing Standards

The US system for crochet hook and knitting needles is, not surprisingly, related.

Here is a table with the metric hook sizes and their respective crochet hook and knitting needle US names.

The table shows an obvious correlation between the crochet hook and knitting needle size names. Since the naming convention of hooks and needles were not standardized, there was difficulties with labeling between different manufactures.

The Craft Yarn Counsel compiled the standardized naming system based on the general industrial standards. Then matched them with the diameter of the hook in millimeters (mm). The metric system, has been widely adopted internationally to make patterns easy to replicate.

Here is a table with the metric hook sizes and their respective international crochet hook names (US, UK/Canada, Japan).

The individual naming systems are very difficult to understand. Especially the US and UK/Canada system where the US names get larger as the size gets larger and the UK names do the opposite.

Most patterns nowadays include the metric sizing for hooks. However, if you're looking at vintage patterns you will need to pay closer attention to the hook sizing!