BOM · 5 min read
An EBOM is the BOM as engineering designs the product: built up like the model, per function and per assembly. An MBOM is the BOM as production makes it: built up per operation and assembly step, with consumables added. They should connect to each other, but they are not the same and they are not allowed to be.
Published 21 September 2026
In short
01 On this page
The engineering BOM comes from the model. The structure follows the design: main assembly, subassemblies, parts. Per line a part number, a description, a quantity and a material.
This is the list you can check the model against, because it should match the product structure one to one.
The manufacturing BOM is built up according to how the product comes about in the workshop. It contains steps that do not exist in the model: a weldment that is treated as a semi-finished product, a part that is blasted and painted, an assembly order that the model does not know.
What is added in the MBOM
The problems do not arise because the two lists differ, but because nobody can point out exactly where the difference comes from.
If the EBOM changes and the MBOM lags behind, things are made on an old build-up. And if the MBOM was built by hand from an export of half a year ago, nobody remembers which lines are deliberately different.
That is why checking starts with the EBOM against the model. If that basis is wrong, every derived list is wrong too, and you only notice in the workshop.
It does not have to be complicated. Two agreements keep it workable.
With BOMproof
BOMproof puts your STEP model, your PDF drawings and your Excel BOM side by side and points out every deviation: with a pin in the 3D model and a balloon on the drawing. You tick off what is correct.
Further reading
Method and corrections
This guide describes in our own words how we carry out a check ourselves. We refer to standards by number; the literal text of the standard is not reproduced here, because it is protected by copyright. Found a mistake? Email info@bomproof.nl: we correct it within a week and put the new date at the top.
02 Frequently asked questions
If you only design and production is elsewhere, you get far with an EBOM. As soon as you make or assemble yourself, an MBOM arises automatically, whether it is called that or not.
The list you provide, against the product structure of your model. In practice that is the EBOM or the BOM on the drawing. Lines that are deliberately not in the model, such as paint or welding wire, show up as lines without a counterpart and you tick those off.
A list in which the structure is visible: subassemblies with their parts below them. The quantity per line then applies per parent assembly and has to be multiplied by it to get the total.
03 Knowledge base
Book a 30-minute demo. Bring one of your own designs and see live how BOMproof checks it.