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What is a BOM bill of materials

Introduction to Bill of Materials (BOM)

A Bill of Materials (BOM) is a comprehensive list of raw materials, components, and assemblies required to manufacture a product. It serves as a crucial document in the manufacturing process, providing detailed information about the product’s composition, including the quantity of each part needed, their descriptions, and sometimes even the cost and supplier details. The BOM is an essential tool for effective material management, production planning, and cost control.

Key Components of a Bill of Materials

A typical BOM includes the following key components:

  1. Part Number: A unique identifier for each component or assembly.
  2. Part Name: A clear description of the part or assembly.
  3. Quantity: The number of units required for each component or assembly.
  4. Unit of Measure: The standard unit used to express the quantity (e.g., pieces, liters, kilograms).
  5. Level: Indicates the hierarchy and relationship between components and assemblies.
  6. Phase: Specifies the stage of the product lifecycle where the component is used (e.g., design, prototyping, production).

Here’s an example of a simple BOM table:

Part Number Part Name Quantity Unit of Measure Level Phase
1 Product XYZ 1 Each 0 Production
1.1 Assembly A 1 Each 1 Production
1.1.1 Component X 2 Pieces 2 Production
1.1.2 Component Y 4 Pieces 2 Production
1.2 Assembly B 1 Each 1 Production
1.2.1 Component Z 3 Pieces 2 Production

Types of Bill of Materials

There are several types of BOMs, each serving a specific purpose in the manufacturing process. Some of the most common types include:

1. Engineering BOM (EBOM)

The Engineering BOM, also known as the Design BOM, is created by the product design team. It contains all the components and assemblies necessary to build the product as designed. The EBOM focuses on the product’s functional requirements and design specifications.

2. Manufacturing BOM (MBOM)

The Manufacturing BOM is derived from the EBOM and is tailored to the specific needs of the manufacturing process. It includes all the components and assemblies required to produce the product on the factory floor. The MBOM may differ from the EBOM due to considerations such as packaging requirements, assembly instructions, and manufacturing constraints.

3. Sales BOM (SBOM)

The Sales BOM, also called the Customer BOM, is a simplified version of the BOM used by the sales team. It includes only the high-level components or assemblies that are relevant to the customer. The SBOM is often used for creating quotes, sales orders, and customer documentation.

4. Service BOM

The Service BOM is used by the after-sales service and maintenance teams. It contains all the components, assemblies, and spare parts required to service and repair the product throughout its lifecycle. The Service BOM ensures that the necessary parts are available for maintenance and repairs, minimizing downtime and improving customer satisfaction.

BOM Hierarchy and Structure

A BOM typically follows a hierarchical structure, with the finished product at the top (Level 0) and the components and assemblies at lower levels. This structure helps to visualize the relationships between the various parts of the product.

Single-Level BOM

A single-level BOM lists all the components and assemblies required to produce the finished product, without showing the relationships between them. This type of BOM is simple and easy to create but does not provide a clear picture of the product’s structure.

Example of a single-level BOM:

Part Number Part Name Quantity Unit of Measure
1 Product XYZ 1 Each
2 Assembly A 1 Each
3 Component X 2 Pieces
4 Component Y 4 Pieces
5 Assembly B 1 Each
6 Component Z 3 Pieces

Multi-Level BOM

A multi-level BOM, also known as an indented BOM, shows the hierarchical relationships between the components and assemblies. It provides a clear understanding of the product’s structure and helps in identifying the dependencies between the various parts.

Example of a multi-level BOM:

Level Part Number Part Name Quantity Unit of Measure
0 1 Product XYZ 1 Each
1 2 Assembly A 1 Each
2 3 Component X 2 Pieces
2 4 Component Y 4 Pieces
1 5 Assembly B 1 Each
2 6 Component Z 3 Pieces

Benefits of Using a Bill of Materials

Implementing a well-structured BOM offers numerous benefits to organizations, including:

  1. Improved Material Management: A BOM provides a clear picture of the materials required for production, enabling better inventory management and reducing the risk of stockouts or overstocking.

  2. Enhanced Communication: By serving as a central document, a BOM improves communication between various departments, such as design, procurement, manufacturing, and sales.

  3. Accurate Costing: A BOM helps in calculating the accurate cost of a product by considering the costs of all components, assemblies, and raw materials.

  4. Streamlined Procurement: With a detailed BOM, procurement teams can easily identify and source the required components and raw materials from approved suppliers.

  5. Efficient Production Planning: A BOM enables production teams to plan and schedule manufacturing activities effectively, ensuring that all necessary components are available when needed.

  6. Simplified Product Updates: When changes are made to a product’s design, a well-maintained BOM makes it easier to identify and update the affected components and assemblies.

Best Practices for Creating and Maintaining BOMs

To ensure the effectiveness and accuracy of BOMs, consider the following best practices:

  1. Standardize Part Numbering: Implement a consistent and logical part numbering system to uniquely identify each component and assembly.

  2. Use Clear Descriptions: Provide clear and concise descriptions for each part to avoid confusion and ensure that the correct components are used.

  3. Maintain Accuracy: Regularly review and update the BOM to reflect any changes in the product’s design, components, or suppliers.

  4. Collaborate with Stakeholders: Involve all relevant stakeholders, such as design, manufacturing, procurement, and sales teams, in the BOM creation and maintenance process.

  5. Leverage Technology: Use BOM management software or PLM (Product Lifecycle Management) systems to create, maintain, and share BOMs efficiently.

  6. Ensure Version Control: Implement version control practices to track changes and maintain a history of BOM revisions.


A Bill of Materials (BOM) is a critical tool in the manufacturing process, providing a comprehensive list of components, assemblies, and raw materials required to produce a product. By creating and maintaining accurate BOMs, organizations can streamline their manufacturing processes, improve material management, and ultimately, enhance product quality and customer satisfaction. Implementing best practices and leveraging technology can further optimize the BOM management process, leading to increased efficiency and productivity.

Frequently Asked Questions (FAQ)

  1. What is the difference between a BOM and a parts list?
    A BOM is a more comprehensive document that includes not only the list of parts but also the hierarchical relationships between components and assemblies. A parts list, on the other hand, is a simpler document that only lists the individual components without specifying the relationships between them.

  2. How often should a BOM be updated?
    A BOM should be updated whenever there are changes to the product’s design, components, or suppliers. It is essential to maintain an up-to-date BOM to ensure accurate production planning, procurement, and costing.

  3. Can a BOM include non-physical items?
    Yes, a BOM can include non-physical items such as software, licenses, or services that are required for the product’s functionality or operation.

  4. What is the role of a BOM in product costing?
    A BOM plays a crucial role in product costing by providing a detailed list of all the components and materials required to manufacture the product. By assigning costs to each item in the BOM, organizations can accurately calculate the total cost of the product, including material, labor, and overhead expenses.

  5. How does a BOM support inventory management?
    A BOM helps in inventory management by providing a clear picture of the components and materials required for production. This information enables organizations to plan their inventory levels, schedule purchases, and minimize the risk of stockouts or overstocking. By maintaining accurate BOMs, companies can optimize their inventory management processes and reduce associated costs.