What is a BOM (Bill of Materials)? and Why do I Need One?

A bill of materials or product structure is a list of the raw materials, sub-assemblies, intermediate assemblies, sub-components, parts, and the quantities of each needed to manufacture an end product. A BOM may be used for communication between manufacturing partners or confined to a single manufacturing plant.

Why is a bill of material important?

BoMs are important because they provide businesses with a complete and accurate picture of the inventory stock required and all the processes associated with creating a single product. In manufacturing a BoM provides a description of the individual components used in production and the relationship between each of those individual parts. In addition, it can include detail of the tools and equipment required for assembly, sub-assembly, and any other consumables needed for the manufacture of a final shippable product.

BoMs are essential tools for eliminating problems in any company that runs lean and continuous improvement processes. They help to reduce errors such as ordering the wrong part or the wrong quantities or similar issues that can lead to costly downtime and production delays.

What does a bill of materials include?

A bill of material should encompass everything required to produce a final product. Detailed instructions, routes, and practices that need to be followed during the manufacturing process can be included within a Bill of Material along with images, diagrams, and links to external files. Generally, a BoM should address:

  • Quantity – the number of parts to be procured or manufactured should be specified for each assembly. Quantity is a primary requirement of any BoM
  • Unit of measurement – to ensure that exact quantities are ordered a BoM should specify the unit of measure for each quantity. For example, per unit, lengths, liters, inches, grams, kilograms, square feet, and cubic-feet
  • BoM level – the BoM level specifies the number or ranking for each part to help identify all the elements of the BoM, whether single or multi-level
  • Part number – a unique part number is assigned to each item for easy reference and for effortless tracking of each part
  • Part name – the unique name of each item combined with a specific part number helps to identify the item easily and effectively
  • Raw material – the BoM should specify the exact quality or type of essential raw material required in the manufacturing process to produce a finished product
  • Description – each part should have a suitable description of the part to help distinguish it from similar parts
  • Notes – the notes simply provide any additional information relevant to the BoM save for the description of parts
  • Images – having images or diagrams of the product being produced, provides a visual representation to help easily understand each component and to cross-reference the BoM details with the image
  • Procurement method – this identifies whether the required part or inventory is purchased externally or manufactured internally

Key benefits:

  • Get the latest status for 550+ million electronic components
  • Integrate data on tens of millions of NSNs and defense parts numbers
  • Get PCN and EOL alerts to manage compliance, obsolescence, and at-risk components
  • Differentiate products faster, optimize inventory, and avoid costly interruptions
  • Satisfy requirements for functionality, lifecycle, price, and compliance

How to Make a Bill of Materials

To generate a bill of materials requires data to be extracted from a planning system, such as an MRP or ERP operating system.  The term ‘A BOM explosion’ is the method used to generate a full list of all the parts including all those in sub-assemblies that are required in order to make a pass of finished goods.  Each individual MRP or ERP system will have its own method of extracting this data.

To put this into context, if planning and production are to make 100 tables as a finished product, they will require components of:

  • 100 x table tops
  • 400 x table legs
  • 400 x brackets for bolting each leg to the table
  • 800 x bolts (2 for each table leg fixing)