This guide will explain how to set the weight of the options correctly.
On the product page of the Shopify, you can set the main weight of your product that will affect the final weight of the customized version of it and will end up in the order and will affect the delivery price.
If you need to set the additional weight to the options you need to switch on Auto-generated products in the App. To find out more about auto-generated products you can read this guide. Once you switched auto-generation on you can put the weight in the option by editing them. This weight will be added to the final weight of the custom product.
If option is connected to the SKU in your product list, the weight set in it will not be added to the final weight of the custom product, so you need to set in the option as well.
However, if you use Bundle builder mode, weight in the option will lead to the error in the final weight. That is why in the Bundle builder mode you need to keep the options empty.
Quantity set both in the Quantity box from General Settings and Quantity customization will not affect the final weight. It is set like this because the Shopify itself will multiply the weight on a check out if the quantity of the product is more then one.
If you need to multiply the weight only of the option it could be done by connecting to another option. To do so you need to set a value of the said option as a multiplier. Example: if the value is set as 2, the weight will be doubled, if the customer chooses the option of 3, the weight will be multiplied by 3.
Weight also can be removed from the cart using the trigger in the General Settings.