My H says #8 in US. Hope this helps.

If you have the silver colored hooks with numbers on them, they are what are called steel hooks, and run much smaller than the hooks that are lettered by size. An H hook would measure narrower than a slender pencil, if that helps. As big around as elbow macaroni maybe?

Do you have one of those needle sizer things? Would that help? Mine has crochet letters on it too. You just stick the needle in the holes, and the smallest one it fits in is the size.

Here is a link that might be useful: Susan Bates Knit Chek

an H hook is 5.0 mm