For anyone looking for this, it took me a while to figure out. Why this is not offered as a simple API call is weird. However, you can do this with the following PHP query:
$get = $wpdb->get_results(" SELECT * FROM ".$wpdb->prefix."newsletter WHERE status='C' ");
echo count ($get);
This queries the Newsletter database and only returns Confirmed subscribers. Then the count line gives you the total array size.
Use a wordpress plugin like XYZ PHP Code to convert that PHP into a usable shortcode. Once you have that done, use the shortcode anywhere you want within your WP site.