How do I store category post count in a variable?

Not sure if using SELECT is best practice, but this will show the number of cats as $numcats

https://perishablepress.com/press/2006/08/28/display-total-number-of-posts/

Unless I’m missing something that only gives you the total count of all posts where I need the count of posts within specific categories.

Thanks

Maybe combining with this to get the category ID

// get the first category id
function get_first_category_ID() {
	$category = get_the_category();
	return $category[0]->cat_ID;
}

to get the postcount of category 3:

<?php
$categories = get_categories('include=3');
$cat3 =$categories[0]->category_count;
?>