Magento Open Source 2.2.x
Product Stock Options

The Product Stock Options configuration determines the default product inventory settings at the product level. The configuration applies to individual products, rather than to the contents of the cart as a whole.

To configure the default inventory settings:

1. On the Admin sidebar, tap Stores. Then under Settings, choose Configuration.
2. In the panel on the left under Catalog, choose Inventory.
3. Expand the Product Stock Options section, and do the following:
a. To activate inventory control for your catalog, set Manage Stock to “Yes.”
b. Set Backorders to one of the following:
  • No Backorders

    To not accept backorders when product is out of stock.

    Allow Qty Below 0

    To accept backorders when the quantity falls below zero.

    Allow Qty Below 0 and Notify Customer

    To accept backorders when the quantity falls below zero, and notify the customer that the order can still be placed.

c. Enter the Maximum Qty Allowed in Shopping Cart.
d. Enter the Qty for Item's Status to Become Out of Stock.
e. Enter the Minimum Qty Allowed in Shopping Cart.
f. In the Notify for Quantity Below field, enter the stock level that triggers notification that the item is out of stock.
g. To activate quantity increments for the product, set Enable Qty Increments to “Yes.” Then in the Qty Increments field, enter the number of the items that must be purchased to meet the requirement. For example, an item that is sold in increments of 6 can be purchased in quantities of 6, 12, 18, and so on.
h. When a credit memo is issued for the item, set Automatically Return Credit Memo Item to Stock to “Yes” if you want to return the item to inventory by default.
4. When complete, tap  Save Config .