If you want to change the default excerpt length of a WordPress site, you can do it using the code below. Paste it in the funtions.php file and update the number in line 9.
remove_filter('get_the_excerpt', 'wp_trim_excerpt');
function custom_trim_excerpt($text) {
global $post;
if ( '' == $text ) {
$text = get_the_content('');
$text = apply_filters('the_content', $text);
$text = str_replace(']]>', ']]>', $text);
$text = strip_tags($text);
$excerpt_length = 75;
$words = explode(' ', $text, $excerpt_length + 1);
if (count($words) > $excerpt_length) {
array_pop($words);
array_push($words, '[...]');
$text = implode(' ', $words);
}
}
return $text;
}
add_filter('get_the_excerpt', 'custom_trim_excerpt');