# Bill Of Materials
At the heart of the Manufacturing system is the **Bill of Materials** (BOM).
The **BOM** is a list of all materials (either bought or made) and operations
that go into a finished product or sub-Item. In ERPNext, the component could
have its own BOM hence forming a tree of Items with multiple levels.
To make accurate Purchase Requests, you must always maintain correct BOMs.
To make a new BOM:
> Manufacturing > Bill of Materials > New BOM
* To add Operations select 'With Operation'. The Operations table shall appear.
* Select the Item for which you want to make the BOM.
* Add the operations that you have to go through to make that particular Item in the “Operations” table. For each operation, you will be asked to enter a Workstation. You must create new Workstations as and when necessary.
* Workstations are defined only for product costing and Production Order Operations scheduling purposes not inventory.
* Inventory is tracked in Warehouses not Workstations.
###Costing of a BOM
* The Costing section in BOM gives an approximate cost of producing the Item.
* Add the list of Items you require for each operation, with its quantity. This Item could be a purchased Item or a sub-assembly with its own BOM. If the row Item is a manufactured Item and has multiple BOMs, select the appropriate BOM. You can also define if a part of the Item goes into scrap.
* This cost can be updated on by using the 'Update Cost' button.
* User can select the currency in the BOM
* System calculates the costing based on the price list currency
### Materials Required(exploded)
This table lists down all the Material required for the Item to be Manufactured.
It also fetches sub-assemblies along with the quantity.
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* To add Operations select 'With Operation'. The Operations table shall appear.
* Select the Item for which you want to make the BOM.
* Add the operations that you have to go through to make that particular Item in the “Operations” table. For each operation, you will be asked to enter a Workstation. You must create new Workstations as and when necessary.
* Workstations are defined only for product costing and Production Order Operations scheduling purposes not inventory.
* Inventory is tracked in Warehouses not Workstations.
###Costing of a BOM
* The Costing section in BOM gives an approximate cost of producing the Item.
* Add the list of Items you require for each operation, with its quantity. This Item could be a purchased Item or a sub-assembly with its own BOM. If the row Item is a manufactured Item and has multiple BOMs, select the appropriate BOM. You can also define if a part of the Item goes into scrap.
* This cost can be updated on by using the 'Update Cost' button.
* User can select the currency in the BOM
* System calculates the costing based on the price list currency
### Materials Required(exploded)
This table lists down all the Material required for the Item to be Manufactured.
It also fetches sub-assemblies along with the quantity.
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