Add a Word Count Column to the WordPress Posts List

/**
 * Add Word Count column to WordPress Posts list
 */
function custom_add_word_count_column( $columns ) {

    $columns['word_count'] = 'Word Count';

    return $columns;
}

add_filter( 'manage_posts_columns', 'custom_add_word_count_column' );


/**
 * Display word count in the custom column
 */
function custom_display_word_count_column( $column, $post_id ) {

    if ( 'word_count' === $column ) {

        $content = get_post_field( 'post_content', $post_id );

        $word_count = str_word_count(
            wp_strip_all_tags( $content )
        );

        echo esc_html( $word_count );
    }
}

add_action(
    'manage_posts_custom_column',
    'custom_display_word_count_column',
    10,
    2
);