Inventory

Hi Loppy22 , (assuming the desktop program) the usual way to do this is have two items.

One is for individual items, and records purchases from suppliers in single item quantities, holds single item inventory and is used for purchase and sales of individual quantities. If your supplier sells you cases, convert the quantity to individual units and change the price accordingly*. 

The second item is for sales of cases, also inventoried, and in this item you create an autobuild entry for (eg) 12 of the first item. This item icarries no stock, so when you record a sale of (eg) one case, AccountRIght will prompt you to order or autobuild; choose autobuild and 12 items will be transferred from the first item to the second. 

* Some people will change the "number of items per buying unit" on the first item to allow them to record purchases in cases. However, suppliers have a habit of changing case sizes, and unfortunately this setting cannot be changed after using it. So I prefer the purcahse method above.