MBOM BASICS · UPDATED 10 OCTOBER 2026
EBOM vs MBOM
An engineering BOM describes a product as designed. A manufacturing BOM describes it as made. Most confusion between them comes from treating one as the other.
Side by side
| EBOM (engineering) | MBOM (manufacturing) | |
|---|---|---|
| Describes | The product as designed | The product as built in the factory |
| Usually owned by | Design or engineering | Manufacturing or production engineering |
| Typical home | CAD or PLM | ERP, MRP or production systems |
| Structure | Follows the design’s assemblies | Follows how the product is made and kitted |
| Sizes | Nominal design dimensions | Cut lengths and panel sizes after deductions |
| Contents | Designed parts | May add fixings, consumables and packaging |
Why they drift apart
The factory rarely builds exactly the design structure. Parts are cut to length, fixings are counted per unit, and assemblies are kitted differently from how they were drawn. Keeping the two in step is part of what PLM and ERP systems are for.
Configured products add another problem
When a product is sold in sizes and options, there is no single MBOM to keep in step. There is a rule for producing one, and that rule has to be applied correctly to every order. It is often the least documented part of the business.
Where FactorySpec fits
FactorySpec is not a PLM system, and it does not transform an EBOM into an MBOM. It holds the rules for producing a configured unit’s MBOM, approved by your product expert, and applies them to each unit’s dimensions and options.
Its output is deliberately flat: components, counts, cut lengths and panel sizes for one unit. Multi-level structure, routings, operations, prices and stock stay in the systems that already own them.
Is it the right tool?
- Yes, if you make a known product family in many sizes and options, and the hard part is working out each unit’s parts.
- No, if you need to manage design revisions, CAD geometry or multi-level assemblies across an engineering team. That is PLM territory.
Read next
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