Bill of Materials (BOM) — Bill of Materials

A Bill of Materials (BOM) — in German Bill of Materials — is the structured list of components, sub-assemblies, raw materials and quantities required to produce one unit of a finished product. The BOM is the central master-data element connecting the engineering, production and procurement views of a product. In an ERP system, BOMs feed MRP, costing, configuration management and shop-floor execution. Without accurate BOMs, MRP produces nonsense and production schedules collapse.

BOM types

• Engineering BOM (EBOM): the design-time structure from CAD, organised by functional groupings
• Manufacturing BOM (MBOM): the production-time structure, often differing from EBOM through alternative parts, packaging, and process steps
• Sales BOM: customer-facing view, often a flat list of features the customer can configure
• Service BOM: spare-parts structure for maintenance and warranty work, may exclude consumables and include service-only items
• Configurable BOM (super-BOM): parametric structure that resolves to a specific variant at order time, common in machine engineering and automotive

Multi-level structure

BOMs in real production are rarely single-level. A finished product has sub-assemblies, each sub-assembly has components, components may have sub-components. Multi-level BOMs nest these into a tree. The deepest practical BOM seen in mid-market manufacturing: 8-12 levels for complex machinery. MRP explosion walks the tree to compute net requirements at every level — computationally heavy, sensitive to lead-time master data at each node.

Common BOM-quality problems

Three recurring problems: (1) EBOM-MBOM-drift — engineering changes don't reach manufacturing structure on time, causing wrong purchases. (2) Phantom assemblies — intermediate levels exist in CAD but not in production, leading to over-counted demand. (3) Quantity errors — especially in volumetric items (paint, lubricants) where unit-of-measure conversions are inconsistent. Resolution requires PLM-ERP integration discipline and regular BOM audits.

Related Topics

• MRP
• ERP
• APS