Add Calculated Column in Admin Product List

currently i can’t find an answer and hope someone can guide and help me to solve my problem.

In the shop i support the qty of a product are packages of items.
We have added a field to the product in which one can save the amount of items inside one package.

My problem is that i have to add a column to the product list containing the total items

eg: qty * items

Would nice if someone has an idea, does’t have to be a complete solution, but would be nice if it is 🙂

Thanks for reading