Say you operate a WooCommerce store where you sell products that are shipped in boxes but want customers to make up their own boxes with different products, by default WooCommerce will only allow you to sell products in the the quantities you set the product up with and the customer will be able to check out with any amount of items in the cart.
For instance if you operate a online wine store with WooCommerce and would like to sell your wine by the bottle but only want customers to checkout if they have quantities selected that would make up a whole box, the following tutorial is for you.
With the code below you can setup your products that each product is a single bottle of wine and then force the customer to add multiples of any 6 products to the cart before they would be able to checkout. If the customer for example adds only 5 bottles to the cart and then tries to checkout they will be presented with a message to order in multiples of 6.
You can even take it a step further and only allow the rule to apply to products with a certain shipping class, this will allow you to sell single bottles as well as cases without having the multiples rule apply to the case products.
To force the customer to add multiples of a certain quantity to the cart before being able to checkout add the following code to your theme’s functions.php file.