Yes, for a completed order you will be able to see which custom box/container was used for the shipment.
The Package detail contains the box/boxes used for the shipment and also the products/products placed into the box.
In the example below the container used for the shipment was 17 x 17 x 20 and the gross weight was 3.
You may have several containers and gross weight variations if multiple products are added to the cart.
We would recommend to add these units at the official shipping carrier when creating a shipping label and paying for the shipping, this will ensure that you match the shipping cost that was provided to the customer on the website.
Click on Package #1