Bill of materials (BOM)

A bill of materials (BOM) is a structured list of everything required to build, assemble, or repair a product. It commonly includes raw materials, purchased parts, subassemblies, consumables, and the quantities, references, and basic attributes needed to support manufacturing, planning, purchasing, and traceability.

Key characteristics

In industrial and regulated manufacturing, a BOM commonly includes:

• Component identification: part numbers, material codes, and descriptions for each item.
• Quantities and units: how many of each item are required per finished unit, with units of measure.
• Structure and levels: parent/child relationships between assemblies, subassemblies, and individual components.
• References to specifications: links to drawings, material specs, or standards that define the item.
• Effectivity and revision fields: optional fields that show which product revision or date range the BOM applies to.

A BOM is typically created and maintained in PLM, PDM, ERP, or MRP systems and is referenced by MES, quality, and document control systems. It is a core artifact for production planning, inventory management, costing, and compliance documentation.

Operational use in manufacturing

On the shop floor, the BOM is used to:

• Determine which parts and materials must be available before work starts.
• Drive pick lists, kitting, and line-side material presentation.
• Support traceability and genealogy by linking actual lots and serials to required components.
• Verify that the correct, approved materials and part revisions are used during production.

In regulated environments, use of the wrong part number, material, or revision relative to the approved BOM is often treated as a nonconformance and may require investigation and documentation.

Common BOM types

• Engineering BOM (EBOM): reflects the product design from engineering, usually structured around functional groupings and design intent.
• Manufacturing BOM (MBOM): reflects how the product is actually built, often restructured into manufacturing steps, work centers, or kit groupings.
• Service or maintenance BOM: lists items relevant to servicing, spare parts, and field repairs.

These BOM views should remain synchronized so that design changes are accurately reflected in manufacturing and service operations.

Common confusion

• BOM vs. routing: A BOM lists what materials and parts are required; a routing or process plan defines how and in what sequence the product is made.
• BOM vs. work instruction: A BOM is a structured data list. Work instructions describe tasks, methods, and checks that may reference items from the BOM.