Update Quantity in Item Table under PO with other custom fields

Update Quantity in Item Table under PO with other custom fields

Is there a way to multiply two custom fields to automatically update the quantity column on an item table under a Purchase Order? I'm looking for fool-proof way to update our quantities of loose items based on the different sizes of packs we receive inventory. For example, I've received 32 packs of an item and each pack has 100 items in it, so our actual quantity increases by 3,200. Looking for a way that my receiver doesn't have to do math when they receive items.