Bill of Materials | What is a Bill of Materials?

What is a bill of materials?

A bill of materials (BOM) is a detailed list of the parts and their respective quantities required to complete an end product.


As your favorite dishes are defined by a recipe that lists out the ingredients in their exact proportions, the breakdown of any equipment into its most basic parts and materials can be listed out through a BOM.

The BOM of equipment can serve different purposes depending on the group that is using it. A manufacturer may use a BOM to schedule production timelines and determine raw material requirements. An engineer might use a version of the BOM to review the design of an equipment and identify possible alternative parts. Maintenance personnel can also use an equipment BOM to identify parts that may require maintenance and keep track of inventory to perform such operations.

Following our cooking analogy, imagine going to the kitchen to prepare a dish without a recipe on hand. You’ll most likely find yourself scrambling for each ingredient every time the need arises. To make things worse, you might even be surprised to realize that your shelves don’t have the spices you need. A similar mess can be expected when performing maintenance work without any idea of what parts the equipment consists of and what materials and spare parts you actually have on hand.

Components of a bill of materials

A typical BOM will include the basics you need to precisely identify the specific parts of a piece of equipment: part number, part name, description, quantity, unit of measure, weight, dimensions, and other specifications of the part.

The extensive list usually appears in a hierarchy denoting any assemblies or sub-assemblies that may comprise the equipment. Some types of BOMs, particularly ones used in engineering, may contain more detail on the design and manufacturing processes that go into the equipment’s construction.

Users of a bill of materials

An equipment’s BOM can enable the maintenance planner to perform their job more effectively and efficiently. By having a clear picture of which parts of the equipment need serviced, the maintenance planner can accurately check the readiness of the team to carry out tasks considering the availability of parts.

When properly updated in a CMMS the speed and accuracy of using BOMs increases dramatically. The planner is able to quickly locate the correct parts or accurately gather purchasing data to prepare for the procurement of required parts. The exact specifications and design criteria that are needed are more easily obtained with greater accuracy.

To take a more proactive approach to managing maintenance activities, the planner can order parts required for future maintenance activities or order critical spares in advance to ensure that they are available. The early detection of spare parts that are going obsolete can also help the planner anticipate changes in the requirements and plan accordingly. The suitability of replacements, if any, can then be reviewed and confirmed ahead of time.

Example of a bill of materials

2004 article in the Journal or Air Transport Management looks into how BOMs are utilized by the aircraft industry in terms of aircraft maintenance and inventory control. Through a survey of procedures done by airline operators and maintenance organizations, it was found that accurately updating BOMs were closely related to carrying out successful materials requirement planning (MRP) processes.

For aircraft maintenance, particularly for rotables repair, a multi-level BOM was determined to be effective. The process is done by entering replacement parts and other repair material into the BOM structure. This step was seen to improve inventory and cost of repairs while enabling the collection of information from maintenance procedures for review and analysis.


Utilizing the equipment’s BOM not only provides a way to perform maintenance tasks accurately, but also enables maintenance personnel to collect data on parts that are being serviced. When coupled with a robust CMMS program, BOMs become an invaluable tool for maintenance planners and maintenance personnel to carry out tasks efficiently.

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