How to Change the Base Unit of Measure (UOM) on an Item

Microsoft Dynamics 365 Business Central restricts changes to an item's Base Unit of Measure (UOM) once transactions have been posted. This is because the base UOM is fundamental to inventory quantities, costing, warehouse operations, and historical accounting records. It is not simply a descriptive field on the Item Card; it defines the unit in which inventory is maintained and tracked.

If you need to change an item's base UOM after transactions exist, a workaround may be available. The recommended approach is to bring the existing item to zero on-hand inventory, resolve any in-process transactions, rename the existing item, create a new item using the original item number and the correct base UOM, and then update any remaining references to the item.

Important: Before proceeding, test this process in a test company and review the potential impact on your inventory, documents, and related records.

Step 1: Review All Existing References to the Item

Before making any changes, identify where the item is currently being used, including open sales orders, purchase orders, component lists, material list lines, and other relevant records.

Use the Item Card and related records to review existing references and identify outstanding quantities or transactions.

• Remove the item from documents and lists wherever possible. Keep a record of each location so you can add the new item back later.
• Resolve partially processed documents. If quantities have already been received or shipped and the transactions cannot be reversed using Undo Receipt or Undo Shipment, complete the related documents by invoicing them, where appropriate.
• Document any references you cannot remove. In some cases, you may be able to leave the item in component lists or other records, provided no inventory movement has occurred for those references (for example, receipt, shipment, or consumption on a shop order). Make a note of each location so you can update it after creating the new item.

 
Step 2: Bring the Existing Item's Inventory to Zero

Use the Item Journal to create a negative inventory adjustment for the existing item, removing all remaining on-hand inventory recorded under the incorrect base UOM.

Before posting the adjustment, verify that the quantity is correct and that any relevant inventory transactions have been resolved.

 
Step 3: Rename and Block the Existing Item

Rename the existing item number by adding a prefix, such as Z or ZZZ. This helps distinguish the old item from active items, moves the item toward the bottom of the item list and frees up the original item number for reuse.

After renaming the item, block it to prevent users from selecting it for new transactions.

 
Step 4: Create the New Item

Create a new Item Card using the original item number.

• Enter the correct Base Unit of Measure.
• Populate all required fields and verify that the item's other settings are configured appropriately.
• Review the item setup before using the new item in transactions.

The new item will now use the correct base UOM while retaining the original item number.

 
Step 5: Update Remaining Documents and Lists

Return to the documents and records identified in Step 1, including open sales orders, purchase orders, material list lines, component lists, and other relevant records.

• Replace references to the renamed item with the new item number wherever necessary.
• If the existing item was left on any in-process documents or lists, those references will still point to the renamed item with the Z or ZZZ prefix. Update them to use the new item number as appropriate.
• Verify that all relevant records reference the new item and that no unintended transactions remain associated with the renamed item.

 
Recommendations Before Proceeding

• Choose a low-activity period. Perform these steps when relatively few users are working in the system. Renaming an item number can update associated entries and may temporarily lock tables, affecting other users.
• Test in a test company first. Rehearse the process in a test environment to identify potential issues before making changes in your live company.
• Verify the results. After completing the process, confirm that the new item has the correct base UOM, inventory quantities are accurate, and relevant documents and lists reference the correct item.

Following these steps can help you transition to the correct base UOM while minimizing disruption to existing inventory records and business processes.