What is a BOM?
A BOM (Bill of Materials) is basically a product’s “ingredient list,” showing all the parts and materials needed to build it.
But different departments look at it from different angles, so we end up with three types: Engineering BOM, Manufacturing BOM, and Cost BOM.
The Differences
- Engineering BOM (EBOM)
- Owner: Design team
- Focus: Which parts are required, with specifications and dimensions
- Example: A laptop design lists the screen, motherboard, keyboard, battery… but not the assembly sequence or material loss.
- Manufacturing BOM (MBOM)
- Owner: Production team
- Focus: How to actually assemble the product, including auxiliary materials, processes, and order of operations
- Example: A laptop assembly needs screws, glue, thermal paste, plus worker steps and testing processes.
- Cost BOM
- Owner: Finance team
- Focus: How much everything costs, including parts, consumables, labor, and waste
- Example: Screen $500, keyboard $100, plus packaging, shipping, and labor—then calculate the total cost of the laptop.
How They Work Together
- EBOM decides “what to make”;
- MBOM shows “how to make it”;
- Cost BOM calculates “how much it costs.”
Think of cooking:
- Engineering BOM = recipe’s ingredient list;
- Manufacturing BOM = the cooking steps + backup ingredients;
- Cost BOM = food market prices, telling you how much the dish really costs.
Common Mistakes
- Using EBOM directly for production, forgetting glue or packaging, leading to errors.
- Not updating Cost BOM, causing wrong pricing.
- Mixing the three BOMs or poor version control, making departments misaligned.
The three BOMs are just different views of the same thing:
- EBOM cares about design completeness;
- MBOM cares about production feasibility;
- Cost BOM cares about financial accuracy.
When each plays its role, products can be made faster, better, and cheaper.