What is a Bill of Materials or BoM?

A Bill of Materials commonly referred to as a BoM, is a complete list of parts that are required to create a finished product. It often has additional information such as supplier, cost, and quantity.

A BoM Includes…

A Bill of Materials is a comprehensive list of all the parts that are required to produce a finished product which is generally constructed layers or hierarchy consisting of top-level assemblies then sub-assemblies and finally individual components. The BoM should include the following important points:

  • BOM Level – This indicates the level of the assembly or part within the hierarchy
  • Part Number – Every element of the BOM needs to have a unique part number including assemblies and sub-assemblies.
  • Revision – This indicates what revision level is currently being used in production
  • Part Name – this is the short form name of each part or assembly
  • Description – This is the part or assembly description which gives more detail about the part
  • Quantity – Each part can be used a number of times in the assembly, each part needs to be listed in the correct assembly and the quantity is shown for each assembly
  • Unit of Measure – This defines the measure in which each part is to be used or purchased, for example, each, kg, drops.

Other options fields could include:

  • Type – This defines is a part is made in house, purchased off the shelf as a standard part or sub-contracted out for manufacture
  • Part Reference – This can be used to identify where a part is used or the type of part it is, for example, PCBA, Hardware, Code
  • Notes – This is just an area against each part where specific notes can be added which can help those using the BoM
  • Price – The current purchase price

And, of course, it identifies the source of each part and the basic commercial information:

  • Supplier company name & contact info
  • MOQ (minimum order quantity)
  • Lead time
  • Payment terms

Without that information, you don’t really have the BOM! If you rely on a manufacturer to order the components, you need to have visibility over all those fields. One benefit is, the manufacturer knows they should not switch to another model or to another source without letting you know. Another benefit is, you can more easily switch to another manufacturer if needed.

Example of a BoM

example of a bill of materials

You’ll also find this video walkthrough of a BOM helpful:


You can also listen to us discuss why the BOM is such an important document, including what it is, problems caused by not having one, how it evolves, how to protect its confidentiality, and more, here in this episode of our podcast:


Our thorough new product introduction process guide, written specifically for hardware startups, will also help guide you through the NPI process and successfully bring your new product to market! Hit the button below to read it (no downloads required):

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