BOM — Bill of Materials
A Bill of Materials (BOM) is a structured list of all components, sub-assemblies, raw materials and quantities required to produce one unit of a finished product. The BOM connects engineering, manufacturing and procurement views and feeds MRP, costing and shop-floor execution in the ERP system.
What does BOM mean
BOM is the standard abbreviation for Bill of Materials. The term describes the hierarchical list that says what goes into what and in what quantity. Whether you read SAP, Oracle, Microsoft Dynamics, NetSuite, Epicor or Infor documentation, the BOM is the same core artifact, even when the user interface labels it slightly differently.
The BOM is the most-referenced master-data artifact in any production ERP: MRP reads it to compute net requirements, costing uses it to roll up product costs, sales-order configuration evaluates it to resolve variants, and shop-floor execution consumes against it. A wrong or missing BOM cascades into wrong purchase orders, wrong production plans and wrong cost calculations — usually noticed weeks later when the variance reports come in.
BOM types in brief
- Engineering BOM (EBOM): design-time structure from CAD, organized by functional grouping
- Manufacturing BOM (MBOM): production-time structure with alternates, phantoms, packaging and shop-floor sequence
- Sales BOM: customer-facing view, often a flat list of selectable options
- Service BOM: spare-parts structure for maintenance and warranty work
- Configurable BOM (super-BOM): parametric structure that resolves to a specific variant at order time, central to engineer-to-order and configure-to-order manufacturing
Multi-level BOMs nest sub-assemblies into a tree — 8–12 levels are typical for complex machinery. The detailed structural and quality discussion lives on the canonical entry: see Bill of Materials.
BOM in MRP and procurement
MRP (Material Requirements Planning) walks the BOM tree to compute gross and net requirements per level. Starting from a sales forecast or production plan at the top level, MRP explodes through every sub-assembly, deducts existing stock and open purchase orders, applies lead times and order quantities, and produces planned purchase orders and production orders at the bottom levels. Wrong BOM quantities directly cause over- or under-ordering — one of the most common reasons for MRP credibility crises in mid-market manufacturing.