Count Posts In WordPress Category

You can make a new WP_Query object, passing args to get some posts that you need a total count of. The object has a $found_posts property, which is not the same as the posts per page count of the posts actually returned by the query. $found_posts is the number of all posts in the DB matching the query criteria. You can make such a query directly from template code, echoing out the value of $found_posts.

$query = new WP_Query(['category_name' => 'books',]);
echo $query->found_posts;

If the template is for listing posts in the same category, you can use the existing WP_Query object’s properties. The existing object is in global $wp_query.

Thank you very much for your input.

But I need the function to be applied to all categories, and not just one. So, there’s no point in specifying a particular category.

How can I achieve that, please?

If you stay with WP methods, it’ll be cumbersome. You’d get a list of all categories, then loop through the list, making a count query for every category.

To get counts within every category, all in one go, you’d need a custom SQL query that uses GROUP BY to get a summary count of posts assigned each category term. You can execute custom queries using wpdb class methods with the global object $wpdb. I’m not very good with SQL, so I cannot provide an example. It does involve JOINing in term_relationships and term_taxonomy tables along with the use of GROUP BY.