Subject in WooCommerce Order Emails

Change The Subject Using the WooCommerce Settings

Go to WooCommerce > Settings > Emails and then click on the email you want to change the subject of. You will find the field Subject. Type in a new subject and click Save.

Change the subject Using the functions.php File

To change the subject line in your order emails, open the functions.php file of your child theme and add the following snippet of code:

/**
 * Change subject in WooCommerce Order Emails using the file functions.php
 * More tips: https://themes.email/woocommerce.html
 *
 *Subject filters: 
 *woocommerce_email_subject_new_order
 *woocommerce_email_subject_customer_processing_order
 *woocommerce_email_subject_customer_completed_order
 *woocommerce_email_subject_customer_invoice
 *woocommerce_email_subject_customer_note
 *woocommerce_email_subject_low_stock
 *woocommerce_email_subject_no_stock
 *woocommerce_email_subject_backorder
 *woocommerce_email_subject_customer_new_account
 *woocommerce_email_subject_customer_invoice_paid
 */

add_filter('woocommerce_email_subject_new_order', 'change_admin_email_subject', 1, 2);

function change_admin_email_subject( $subject, $order ) {
	global $woocommerce;

	$blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);

	$subject = sprintf( '[%s] New Customer Order (# %s) from Name %s %s', $blogname, $order->id, $order->billing_first_name, $order->billing_last_name );

	return $subject;
}