Also called parts list, EBOM, MBOM
What is a bill of materials?
The full list of what goes into a product, level by level, with quantities.
What else it is called
- Other names
- parts list, EBOM, MBOM
- In French
- nomenclature
Related entries
Understanding bill of materials
The list of everything that goes into a product, with quantities, usually structured so that a top-level assembly points at sub-assemblies which point at parts and raw material. The structure matters. Change a component two levels down and the list tells you every assembly affected, which is how an engineering change gets costed.
The failure mode in a small manufacturer is rarely that no list exists. It is that three do - engineering’s drawing-derived version, purchasing’s buying list, and the one the floor actually builds from, which contains the substitution somebody made in 2023 and never recorded. Each is right about something and none is authoritative, so every system built on top of them inherits the disagreement.
Two distinctions worth keeping straight. An engineering bill of materials describes the product as designed; a manufacturing bill describes it as built, including packaging, consumables and the intermediate states the floor actually stocks. Confusing the two produces costing that is confidently wrong.
In practice
Before any software project that touches production, establish which copy is the one that governs. Projects that skip this question spend their second month discovering the answer.
Frequently asked
What is the difference between an engineering and a manufacturing bill of materials?
The engineering version describes the product as designed, organized the way the designer thinks about it. The manufacturing version describes it as actually built, organized by the sequence of assembly and including packaging, consumables and sub-assemblies you stock. Costing and planning need the manufacturing version.
Who should own the bill of materials?
One named function, with a controlled change process - normally engineering, with purchasing and production consulted on changes. Shared ownership means no ownership, and the symptom is three versions.