You have the ability to enter quantities per size when filtering for products and not just the category. As you see in the first screen shot, instead of a check mark for sizes, you are able to insert a quantity beside the sizes.
Now you are able to search by specific quantities of the size. For an example, I am searching for all products that have quantity of 1300 in size Small.
This will help you placing orders when you are in need of specific quantities orders.