The calculation method of the best purchase quantity and the best stock quantity of single product

The calculation formula of purchase quantity of single goods is generally:
The best purchase quantity = Low limit ≤ (planned dosage + inventory low limit – on-hand inventory) ≤ inventory High-limit
which
Inventory low limit must be guaranteed, inventory high-limit in the procurement for reference only.
On-hand inventory = existing physical stock + in-transit inventory
Existing physical stock = Posted Inventory
Plan dosage = (daily sales x estimated days in transit + customer's latest order) x management error Rate
The management error rate should be greater than 1.

Note: The calculation formula of the best stock of single product is:
Best stock = Stock low limit ≤ (existing stock-defective) ≤ inventory high-limit
which
Existing stock = existing physical stock + in-transit quantity
Existing physical stock = Posted Inventory

In transit: a stock in transit that has been issued by purchase plan or purchase order and has not yet arrived.