Multiple units in purchase

Dealer distributors need multiple units such as a product that has a box and several pieces, one box equals 12 pieces.

If he wants to purchase this product with several pieces in one line.

We also need here to display stock in different units and total stock by the base unit, such as "10 boxes 2 pieces total stock 122 pieces" (All invoices, packaging slips, and all documents need to display this information).