What’s a Bill of Materials (BOM)?

Bill of Materials (BOM) Defined

A Bill of Materials, or BOM, is an industry term for a comprehensive list of everything required to build a product, including the raw materials, components, sub-assemblies, intermediate assemblies, parts, and exact quantities of each.

Its Importance to Businesses

A BOM is a vital part of a production order, allowing manufacturing partners or single manufacturing plants to reserve the sufficient amount of materials they have in-stock, or make an order for any components that they don’t have in-stock. The BOM ensures that everything needed is properly accounted for throughout the manufacturing process, acting as a detailed blueprint for all communication.

Creating a well-structured Bill of Materials is crucial for a range of industries, especially manufacturing, construction, and engineering, as it ensures projects are completed in a streamlined manner with as little waste as possible. They tend to include the following:

• BOM level: The hierarchical position of a component, showing how it fits into the final product.
• Part numbers: The unique number for each component, for easy identification.
• Description: Brief details about the components, such as size and unit of measurement.
• Unit cost: The price of a single component.
• Quantity: The exact number of components needed.
• Total cost: The price of the total number of components.
• Procurement details: Whether a component is purchased or manufactured in-house.

Examples of BOMs

Bill of Materials complexity depends on the industry and product being manufactured. Here are some examples of how the components listed may differ between trades:

• Smartphone manufacturing: A BOM for an electrical item such as a smartphone will include components such as battery, processor, camera module, screen, circuit boards, and assembly instructions.
• Car manufacturing: BOMs in the automotive industry detail thousands of parts, from bigger components like engine and transmission, to individual nuts and bolts required.
• Mass food and beverage production: A restaurant BOM will outline all ingredients and quantities needed to create specific menu items, including exact amounts and costs.
• Clothing production: Apparel BOMs will include everything required to create a final product, including fabrics, threads, zippers, individual buttons, and necessary equipment.
• Construction: A BOM in the building industry will include the necessary materials for construction – such as concrete, steel beams, plumbing, wiring, structural beams, and even finishing elements like paint and tiles.

Types of Bill of Materials (BOM)

There are two main types of BOMs: Engineering Bill of Materials (EBOM) and Manufacturing Bill of Materials (MBOM). Both are required in the production process, though they come at different stages. The EBOM comes first, in the design and development stage, and the MBOM comes second, to be used in the production process.

Engineering Bill of Materials (EBOM)

An EBOM is created to reflect a product’s functional and structural design in the development phase of a product. It often includes multiple revisions as the design evolves, and outlines the components and subassemblies as defined by an engineering team. It’s a foundational BOM, used as a basis for creating an MBOM in the next stage of production.

Manufacturing Bill of Materials (MBOM)

An MBOM includes all the information needed to manufacture a product, and is a key part of the production process. Unlike an EBOM, this type of BOM also outlines any additional elements used in the manufacturing process, like packaging, consumables, and even manufacturing instructions.

Additional points to note about BOMs

It’s important to keep Bills of Materials accurate in order to avoid excess cost, waste, and time in the production process. Here are some useful things to keep in mind when it comes to understanding them:

• There are multiple structures: BOMs can be either single-level (purely listing components, with no hierarchy) or multi-level (including a structured breakdown of all subassemblies and parts in more complex projects).
• They help with inventory control: A well-managed BOM will prevent over-purchasing or shortages, allowing manufacturers to accurately track stock levels.
• They are vital for cost estimations: BOMs are vital in cost forecasting – enabling accurate predictions for production.
• They support quality control: Maintaining a good BOM will support a product’s quality control, ensuring it meets regulatory standards and compliance requirements from the start.
• They improve cross-team communication: The BOM acts as a key part of communication and collaboration – aligning teams across engineering, procurement, and manufacturing.
• They aren’t set in stone: BOMs are dynamic, updating throughout the production process to reflect any design changes, substitutions, or supplier modifications.