function wt_get_category_count($input = '') {
global $wpdb;
if($input == '') {
$category = get_the_category();
return $category[0]->category_count;
}
elseif(is_numeric($input)) {
$SQL = "SELECT $wpdb->term_taxonomy.count FROM $wpdb->terms, $wpdb->term_taxonomy WHERE $wpdb->terms.term_id=$wpdb->term_taxonomy.term_id AND $wpdb->term_taxonomy.term_id=$input";
return $wpdb->get_var($SQL);
}
else {
$SQL = "SELECT $wpdb->term_taxonomy.count FROM $wpdb->terms, $wpdb->term_taxonomy WHERE $wpdb->terms.term_id=$wpdb->term_taxonomy.term_id AND $wpdb->terms.slug='$input'";
return $wpdb->get_var($SQL);
}
}

<?php echo wt_get_category_count(); ?>

<?php echo wt_get_category_count(1); ?>

<?php echo wt_get_category_count('hello-world'); ?>

<?php echo strip_tags(wp_list_categories('include=3&hide_empty=0&use_desc_for_title =0&echo=0&show_count=1&style=none&hierarchical =0&title_li=')); ?>

<?php
// 將以下category-name改成你的分類別名即可
echo get_category_by_slug('category-name')->count;
?>

<?php
// 將以下cat_ID改成你的分類ID即可
echo get_category(cat_ID)->count;
?>