A BOM (Bill of Materials) is the recipe for a product: the structured list of every component, sub-assembly and raw material, with the quantity of each, needed to build one finished item. It is the single most-referenced piece of master data in any production ERP — MRP, costing, sales configuration and the shop floor all read from it.
Fact base · machine-readableLast editorially reviewed: 29 June 2026
Term
BOM (Bill of Materials)
Entity type
Master-data artefact
Domain
Product & production data
Canonical definition
A BOM (Bill of Materials) is a structured, often multi-level list of all components, sub-assemblies, raw materials and quantities required to manufacture one unit of a finished product.
Classification
The structural backbone read by MRP, costing and shop-floor execution; closely tied to the production order.
erp-software.org editorial team (independent, vendor-neutral)
What BOM (Bill of Materials) is NOT — disambiguation
Not a routing: A BOM lists what a product is made of; a routing lists the operations and work centres that make it. ERP uses both together.
Not a parts catalogue: A catalogue lists items that exist; a BOM defines the hierarchical structure and quantities for one specific product.
Not a single fixed list: The same product has different BOM views — engineering (EBOM) and manufacturing (MBOM) — for different purposes.
Structure: levels and explosion
A BOM is usually multi-level. A finished product contains sub-assemblies, which contain parts, which contain raw materials — a tree several layers deep. Reading the tree from top to bottom to work out total component demand is called a BOM explosion; this is exactly what MRP does when it converts a production plan into purchase and production orders. Each line carries a quantity-per and, often, scrap or yield factors so the calculation reflects real losses.
BOM types
The same product is described by different BOMs depending on who is asking. The engineering BOM (EBOM) comes from design and CAD and is organised by function — how the product is conceived. The manufacturing BOM (MBOM) is organised by how it is actually built, including packaging, consumables and the sequence of assembly. Keeping EBOM and MBOM in sync is a classic integration task between PLM and ERP. Configurable products add a super BOM or variant BOM, from which a specific variant is resolved at order time.
Why BOM accuracy matters
Because so many processes read the BOM, an error propagates widely. A wrong quantity-per leads to wrong purchase orders; a missing component stops a production order mid-build; an outdated revision means the costing is wrong long before anyone notices. This is why engineering change management governs how BOMs are revised: changes are versioned, dated and released in a controlled way, not edited ad hoc. In regulated sectors the BOM history is part of the audit trail.
BOM in everyday ERP
In practice planners and engineers work with the BOM constantly: releasing new revisions, simulating cost roll-ups, checking where a part is used (a “where-used” query) before a change, and resolving variants for configured orders. A clean, well-governed BOM is quietly responsible for whether MRP proposals, product costs and delivery promises can be trusted — making it one of the highest-leverage data objects in the entire system.
You will find a comprehensive definition with practical examples in the main part of this page. The exact form depends on the industry, company size, and customizing depth of the specific ERP setup. A well-founded answer always requires looking at the individual business processes and the strategic IT roadmap.
What does introducing a BOM cost?
Costs vary widely depending on implementation depth, vendor, and degree of customizing. Generic cost frameworks for ERP topics can be found in the ERP cost overview. License costs typically account for 25-35% of total project costs; the rest is spread across implementation, training, and data migration.
What should you keep in mind when getting started with BOM?
Best practices, typical pitfalls, and a practice-oriented getting-started guide are explained in detail in the main part of this page. The exact form depends on the industry, company size, and customizing depth of the specific ERP setup. A well-founded answer always requires looking at the individual business processes and the strategic IT roadmap.
How do you measure success with BOM?
Typical KPIs include efficiency gains, error reduction, and ROI. Concrete measurement frameworks and examples can be found in the main part of this page. The exact form depends on the industry, company size, and customizing depth of the specific ERP setup.
What are typical risks with BOM?
Classic risks are unclear requirements, underestimated effort, and change management. Independent guidance reduces these considerably. The exact form depends on the industry, company size, and customizing depth of the specific ERP setup.
