Crochet Hook and Knitting Needle Size Conversion
Metric is the most accurate measurement for crochet hooks because the letter/number system can get wonky and then you've got US vs UK/Canadian, and to make matters weirder, the lace hooks come into play and then your brain explodes. Anyway, here is the regular ol' yarn crochet hook conversion chart.
Now, ignore the below conversion chart unless you actually need it and are using steel/lace hooks. I have never made lace in my life, but I do have a set of these. Fun fact: I also have some hooks that have UK numbers, so talk about confusing sometimes!
I did not forget the knitters! I actually have a lil plastic gauge calibration tool where you can size your needles as well. I came across this hedgehog one the other day, and they really come in handy if you don't have a labeled case for your needles or you mess up and don't put things back where they go all the time. Ahem. Not calling anyone out. Ahem.