Purchase UoM (Unit of Measure) and Conversion in Purchase Transactions
In ERPNext, every item has a default Stock Unit of Measure (UoM) used for inventory tracking.
However, the unit in which items are purchased from suppliers may differ from the stock unit.
ERPNext allows you to use a separate Purchase UoM in procurement transactions while maintaining accurate stock valuation in the default stock UoM.
1. Understanding the Scenario
An item may be stored in one unit but purchased in another.
- Example: Pens are stocked in Nos, but purchased in Box.
- Example: Sand is stocked in Kg, but purchased in Truckloads.
This flexibility allows businesses to align purchasing with supplier packaging formats.
2. Setting Purchase UoM in Purchase Order
Step 1: Update UoM in Purchase Order
In the Purchase Order, two UoM fields are available:
- UoM (Purchase UoM)
- Stock UoM
By default, both fields fetch the item’s stock UoM. You can change the Purchase UoM to match supplier packaging (e.g., Box).
The Purchase UoM is mainly used for supplier reference and printing purposes.
Step 2: Define Conversion Factor
The UoM Conversion Factor defines how many stock units are contained in one purchase unit.
Example:
- 1 Box = 20 Nos (Pens)
If you purchase 1 Box, ERPNext automatically converts it into 20 Nos in stock terms.
3. Stock Quantity Calculation
Stock quantity is always calculated in the Stock UoM, regardless of the Purchase UoM used.
This ensures accurate inventory tracking and valuation in ERPNext.
4. Stock Ledger Posting
All stock ledger entries are posted only in the Stock UoM of the item.
Even if procurement is done in different units (Box, Pack, Truck), ERPNext converts everything into the base stock unit before updating inventory.
It is important to maintain correct conversion factors to avoid inventory mismatches.
5. Setting Conversion Factor in Item Master
You can define multiple purchase UoMs directly in the Item Master.
Under the Purchase section, ERPNext allows you to map:
- Allowed Purchase UoMs
- Conversion Factors for each UoM
This ensures consistent and error-free conversions during purchasing.
6. Benefits
- Supports flexible purchasing units
- Ensures accurate stock tracking
- Reduces manual conversion errors
- Aligns procurement with supplier packaging
- Maintains correct inventory valuation
