Crochet Hook Sizing Systems

There are many systems for crochet hook sizing! I'm based in the US so I'll go over the ones here first!

But... unfortunately they aren't universal. Even the US uses two different labeling systems. The first is simply called "US Sizing" and the second is "Metric Sizing".

US sizing has both number and alphabetic labels. US sizing is seemingly arbitrary but is based on a more antiquated standardization system.

Metric sizing is simply the diameter measurement of the hook. Because of that, if in a bind, you can use a caliper to measure the size! They also make "hook gauges" specifically to measure the diameter of crochet hooks.

I prefer metric sizing, as it is often used in both pattern instructions and hook-inscribed labels.

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Here is a handy chart which shows the translation between US and metric sizing.

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Different hook sizes are very important for a project. Hook sizing generally is a match to the size of the yarn used. This allows the project stitches to be tighter (or looser). The CONSISTENCY for hook size in a project is essential. If you're setting a project down for an extended period of time, make sure to log what hook you're using!