WooCommerce: Sync Product Quantities @ Cart

This snippet will help you synchronize all your cart items’ quantities with a given product ID quantity. When you add a second product to cart, therefore, it will get the same quantity of your product ID. Also, if you update the quantity of product ID, the other cart item quantities will automatically update accordingly.

Applications are quite niche, but it’s great to learn how to programmatically set the quantity of a cart item. As usual, each snippet of this website has got something that sooner or later you may need to use. Enjoy!

PHP Snippet: Synchronize Product ID Quantity And Other Item Quantities @ WooCommerce Cart

Note: you have to specify your “master_product_id” inside the snippet. This is the reference product. All the other products in the cart will sync with its quantity.

/**
 * @snippet       Sync Cart Item Quantities
 * @how-to        Get CustomizeWoo.com FREE
 * @author        Rodolfo Melogli
 * @compatible    WooCommerce 4.0
 * @community     https://businessbloomer.com/club/
 */
   
add_action( 'template_redirect', 'bbloomer_sync_cart_quantities' );
   
function bbloomer_sync_cart_quantities() {
    if ( WC()->cart->is_empty() ) return;
	$master_product_id = 20;
	$in_cart = false;
	foreach( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
		if ( $master_product_id === $cart_item['product_id'] ) {
			$qty = $cart_item['quantity'];
			$in_cart = true;
			break;
		}
	}
	if ( ! $in_cart ) return;
	foreach( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
		if ( $master_product_id !== $cart_item['product_id'] ) {
			WC()->cart->set_quantity( $cart_item_key, $qty );
		}
	}     
}

Where to add custom code?

You should place custom PHP in functions.php and custom CSS in style.css of your child theme: where to place WooCommerce customization?

This code still works, unless you report otherwise. To exclude conflicts, temporarily switch to the Storefront theme, disable all plugins except WooCommerce, and test the snippet again: WooCommerce troubleshooting 101

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Rodolfo Melogli

Business Bloomer Founder

Author, WooCommerce expert and WordCamp speaker, Rodolfo has worked as an independent WooCommerce freelancer since 2011. His goal is to help entrepreneurs and developers overcome their WooCommerce nightmares. Rodolfo loves travelling, chasing tennis & soccer balls and, of course, wood fired oven pizza. Follow @rmelogli