Production/Inventory

I have a workbook that tracks inventory, but I would like to update it with a
formula to help me track the materials used to create my inventory.

Example: Let's say a product is packed at 100 pcs per box.
Each day I pack different quantities. How do I get this formula to track
how many boxes are used for the quantities packed? The box should not be
counted as a full box until it is a full 100 pcs.

Day 1 - 500 pcs
Day 2 - 325 pcs
Day 3 - 619 pcs

I want to make sure I don't run out of boxes, so I would like to have a
buffer of say 500 boxes and have it flagged at that time to order more.