In Estonia we measure the size of crochet hooks in millimetres, but USA and UK have their own systems, which can be a bit confusing, made worse by the fact that different manufacturers' hooks can have a slight difference in the size as well.
When it comes to very small crochet hooks, aka thread or steel hooks, it looks like manufacturers haven't found a system they all like, so each one uses their own size charts. Which is why I haven't included them here.
I put together a little comparison chart based on the most common crochet hook brands (ADDI, Tulip, Clover, Pony), so you can find the right hook for any project, no matter where your pattern is from.
