Exploring the Differences Between BOM, eBOM, mBOM, & aBOM
Implementing a Bill of Materials (BOM) management software can significantly improve operational efficiency for teams focused on engineering, manufacturing, and testing physical products. A recent McKinsey & Company report showed that digitizing work instructions, part management, and inventory tracking leads to a 15-30% increase in productivity and throughput.
At Epsilon3, we’re passionate about building web-based solutions that help innovative teams streamline and standardize engineering, assembly, and test workflows. Being uniquely positioned to support engineers, technicians, and operators—as opposed to just supply chain and finance teams like most legacy resource planning (ERP) systems—we often get asked, "What’s the difference between BOM, eBOM, mBOM, and aBOM?"
The short answer is that they serve distinct roles in a product's lifecycle. This article breaks down these variations while highlighting how an integrated manufacturing operations management solution can optimize operations, preventing costly delays and quality issues.
What is a Bill of Materials (BOM)?
A Bill of Materials (BOM) is a comprehensive list of parts, components, assemblies, and raw materials required to build a product. It serves as a roadmap for engineers, manufacturers, and supply chain teams, ensuring that every necessary component is accounted for and available. BOMs can vary in complexity depending on the product, industry, and intended use, but they typically include part numbers, descriptions, quantities, and sometimes sourcing details.
While "BOM" is a broad term, different types of BOMs exist to serve specific purposes throughout a product’s lifecycle. These include:
Engineering Bill of Materials (eBOM)
Manufacturing Bill of Materials (mBOM)
As-Built Bill of Materials (aBOM)
Engineering Bill of Materials (eBOM)
The Engineering BOM (eBOM) is developed during a product's design phase. Engineers typically create it using design and Product Lifecycle Management (PLM) systems. The eBOM defines the product's structure based on design specifications and functional requirements.
Key Characteristics of eBOM:
Created by engineers (e.g., design, hardware, aerospace, mechanical, structural, electrical).
Includes components based on product design, functionality, and specifications.
Typically organized according to how the product is conceptualized rather than how it will be manufactured and built.
Often contains documentation, drawings, and reference materials.
How eBOM Relates to Other BOMs:
The eBOM forms the foundation for the mBOM, which translates design intent into manufacturing reality.
It is primarily used in engineering teams before a product moves into manufacturing.
Any design changes or iterations are reflected in the eBOM before being pushed downstream.
EXAMPLE: In the aerospace industry, an eBOM for an aircraft might include detailed design specifications for high-level assemblies such as wings, fuselage, avionics, and landing gear.
Manufacturing Bill of Materials (mBOM)
The Manufacturing BOM (mBOM) is a derivative of the eBOM that details the components, subassemblies, and materials required for manufacturing a product. Unlike the eBOM, which focuses on design, the mBOM is structured to support manufacturing processes, assembly operations, and supply chain logistics.
Key Characteristics of mBOM:
Developed for use by manufacturing teams.
Includes required components, parts, tools, work instructions.
Structured based on how the product will be assembled during the production process.
Ensures alignment between procurement, inventory management, and production planning.
How mBOM Relates to Other BOMs:
The mBOM is derived from the eBOM but tailored to the assembly and production process.
It serves as a bridge between product design and manufacturing operations.
The aBOM is based on the mBOM but reflects the final product after assembly.
EXAMPLE: In an electric vehicle or aircraft factory, an mBOM would include battery modules, power electronics, chassis components, fasteners, and detailed assembly instructions for production line workers.
As-Built Bill of Materials (aBOM)
The As-Built BOM (aBOM) represents the actual configuration of a product after it has been manufactured, assembled, and possibly modified. Unlike the eBOM and mBOM, which define what should be built, the aBOM records what was actually built, including any substitutions or deviations.
Key Characteristics of aBOM:
Captures real-world changes made during the manufacturing and assembly processes.
Used for quality control, issue tracking, maintenance, and service records.
Helps track version control, future modifications, or repairs.
Essential for industries where traceability and compliance are critical (e.g., aerospace, defense, robotics, energy, medical devices).
How aBOM Relates to Other BOMs:
The aBOM is a post-production version of the mBOM, reflecting any changes during assembly.
It is essential for maintenance teams, field engineers, and service personnel.
It provides a historical record of product configurations, which is crucial for long-term support.
EXAMPLE: In the space industry, an aBOM for a satellite would include every actual part and component installed, along with any modifications or substitutions made during assembly, integration, and test. Check out our latest customer case study with Redwire Space for a deeper look at how Epsilon3 can help track aBOMs.
Reasons to Implement Web-Based BOM Management
Managing BOMs effectively is crucial for physical product development. Companies risk production delays, procurement errors, compliance issues, and increased costs without a clear and well-structured BOM system. An integrated BOM management solution, like the one we offer at Epsilon3, helps organizations:
Maintain version control across eBOM, mBOM, and aBOM.
Improve collaboration between engineering, manufacturing, and supply chain teams.
Enhance traceability for regulatory compliance and quality assurance.
Reduce errors and inefficiencies in production planning and execution.
By leveraging Epsilon3’s advanced manufacturing operations management platform, companies can ensure their production data is accurate, up-to-date, and seamlessly connected across different teams and processes. System integrations, role-based permissions, and advanced cybersecurity controls make Epsilon3 an excellent choice for cutting-edge product development.
A McKinsey & Company research paper identified six key impacts digital transformation has on manufacturing operations.
✔ 15-20% inventory-holding cost reduction
✔ 15-30% labor productivity increase
✔ 30-50% machine downtime reduction
✔ 10-30% throughput increase
✔ 10-20% cost-of-quality improvement
✔ 85% forecasting accuracy improvement
