A bill of materials (BOM) is a comprehensive inventory of the raw materials, assemblies, subassemblies, parts and components, as well as the quantities of each, needed to manufacture a product. This facilitates immediate reduction in stock of the item automatically. This process of listing the items that make up another item is made possible in Tally by enabling the Bill of Materials Facility.

Bill of Material (BoM) is created only for those items that are being assembled in-house. Therefore, you need to specify a BoM at the time of creating a Stock Item or while altering the stock item. For trading items, you do not need a BoM.