wp3 – finding category number?

If you are wanting to get the category id from the category name in php, use get_cat_ID().

If what you want is to manually find the id, go to Admin->Posts->Categories and hover over a category name. Look for tag_ID=nn in the bottom browser status bar. If you can’t see tag_ID= because the URL is too long, edit the category and look for it in the top browser address bar. You may have to click in the address bar and press ‘End’ to get to the end of the URL.

So would

https://www.domain.com/wp-admin/edit-tags.php?action=edit&taxonomy=category&post_type=post&tag_ID=1

mean that the category id is “1”?

??

Yes, that is right.