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Bill of Materials Definition Simple

A bill of materials is a centralized source of information that lists all components required to create a product. These can be raw materials, elements, components, assemblies or sub-assemblies used in the manufacture of a final product.

BOMs can be created by various teams across the organization including engineering, design and manufacturing. This helps eliminate inventory inaccuracies and production delays, resulting in cost savings.


Just as you can’t construct a building without a blueprint or cook a recipe without a list of ingredients, manufacturing and production requires a clear plan to make things work. The key to a smooth and efficient process is the bill of materials (BOM). BOMs are comprehensive inventories of components, raw material assemblies, sub-components and parts used to create a finished product. They also contain procurement instructions. A BOM may be shared among manufacturing partners or confined to a single plant. Other terms for a BOM include assembly component list, product recipe, and product structure.

A BOM lists the raw materials, elements, components, assemblies and parts that go into a final product, as well as the quantities of each item. They can be for any type of product, from a simple window to an entire piece of machinery or equipment. The information in a BOM can be passed on to manufacturing operations and suppliers to help them estimate cost, prepare purchase orders and track production progress.

The format of a BOM depends on the needs of your business. It can define products as they are designed (engineering bill of materials, or EBOM), as they are sold and shipped to customers (sales BOM, or MBOM) or as they are built in your factory (manufacturing BOM, or MBOM). There are several different types of BOMs, from a single-level list to a multi-level hierarchy.


The purpose of a bill of materials is to record the raw materials, components, subassemblies, and assemblies needed to create a finished product. It’s also used for other production planning tasks, such as estimating costs, monitoring inventory, and ensuring that third-party contract manufacturers are using efficient and accurate production methods. A well-executed BOM can save a company revenue and prevent investigations, purchasing issues, and production delays.

A BOM can be used for any type of manufacturing, including the building of physical products, software, or even services. It can be created on a computer-aided design system (CAD) or in a spreadsheet program. A configurable BOM is a type of BOM that lists all the possible options for an end product, such as different color schemes for a pair of jeans.

A BOM is usually structured in a hierarchical format, with the top-level part representing the finished product and the lower-level parts being sub-assemblies, subcomponents, or individual components. The BOM can be single-level or multi-level. A multi-level BOM displays the relationship between assembly and sub-assemblies by indenting one level below the other. This is commonly called a “parent-child” relationship. The BOM can also include notes that provide other information, such as alternate suppliers or specifications that a component must meet. BOMs can be stored in an electronic data storage system, or manually entered into a spreadsheet.


BOMs are used in many business operations to provide details on the components and parts needed to assemble a final product. These details help businesses plan, estimate costs, manage inventory, monitor production and quality and maintain documentation. They also make it possible to reduce waste and stay ahead of material shortages and other supply chain problems.

The types of BOMs used by a company can vary depending on the industry and type of product being produced. For example, an engineering bill of materials (EBOM) is a list of the parts, components, and sub-assemblies that go into an engineering product. It may be prepared by a technical designer or by using computer-aided design. An EBOM can also contain the alternative and substitution part numbers and drawing notes.

A manufacturing bill of materials, on the other hand, includes all the parts and assemblies required to construct a finished product ready for shipping. It may include packaging materials, assembly instructions, and other related processes. In some cases, a manufacturing BOM can be considered a “shopping list” for a specific product.

A well-executed bill of materials can prevent costly and time-consuming mistakes such as inventory inaccuracies, production delays and the need for expediting charges. The accuracy of the information in a BOM can also ensure consistency and quality across multiple production runs. Creating and maintaining a BOM requires the collaboration of multiple departments within a company, including engineering, purchasing, and materials management.


Bill of materials, or BOMs are an essential tool for any manufacturing business. They provide a comprehensive list of the raw materials, sub-assemblies, components, assemblies and parts – along with their required quantities – needed to manufacture a final product. A well-written BOM can also help companies reduce errors during the procurement process and improve inventory tracking.

BOMs can be formatted in various ways depending on the type of product. For example, a drawing BOM is a part list placed directly in the drawing of a specific assembly. It can contain part names, descriptions and quantities as well as the part number and description. A single-level BOM lists all the components that are used in a particular assembly and does not include any sub-assemblies or raw materials.

A multi-level BOM, or an indented BOM, is a more detailed breakdown of the components that make up a finished product. It can be arranged in a parent-child relationship with the top-level product at the highest level, followed by all of the assemblies and sub-assemblies that are needed to produce it.

Creating a bill of materials can be a complex task, especially for large products with thousands of parts. However, it is essential to have a clear and accurate BOM in order to track the product through the production process and prevent costly mistakes. These mistakes can include purchasing the wrong component, production delays due to missing components or additional expediting charges as a result of late deliveries.