Add a class to post_class if more than one post shares same meta_value_num
add_filter(‘post_class’, function($classes){ global $wp_query; static $meta = array(); // first call gathers meta values if(!$meta) foreach($wp_query->posts as $post) $meta[$post->ID] = get_post_meta($post->ID, ‘your_meta_key’, true); // $wp_query->post should be the global (current) $post object $this_meta = $meta[$wp_query->post->ID]; if($this_meta){ $counts = array_count_values($meta); if($counts[$this_meta] > 1) $classes[] = ‘your_class’; } return $classes; }); (untested)