Bill of Materials (BOM): Definition, Functions, Types, and Examples
A Bill of Materials (BOM) is one of the most critical pieces of data in the manufacturing process. A BOM helps companies identify the materials, components, and exact quantities required to produce a product in a structured manner.
Without an accurate BOM, companies risk experiencing material shortages, incorrect component usage, over-purchasing, and inconsistencies in final production outputs. Therefore, BOM management serves as a crucial foundation in production planning and control.
What Is a Bill of Materials (BOM)?
A Bill of Materials (BOM) is a structured list containing all raw materials, components, subassemblies, and quantities needed to manufacture a product.
A BOM can be compared to a recipe in the manufacturing process. If a product requires five different components, the BOM details which components are used, the quantity of each, the units of measurement applied, and how each component relates to the final product.
Within a manufacturing company, the BOM serves as a reference point for various departments, such as production planning, purchasing, warehouse, production, engineering, quality control, and finance.
BOM data can also be integrated with systems like a Manufacturing Execution System (MES) and a Warehouse Management System (WMS), such as those provided by Prieds, so that material requirements from the planning phase to actual usage can be managed in a more structured manner.
Why Is a Bill of Materials Important?
Production activities require numerous materials and components that must be available in the right quantities and at the right time. Without a clear list of requirements, companies find it difficult to determine how much material should be purchased, stored, and prepared for production.
A BOM provides the structure that forms the basis for material requirement calculations. When a company wants to produce 1,000 units of a product, the system can use the BOM to calculate the exact quantity needed for every component.
In addition to supporting material planning, a BOM helps maintain consistency in production outputs. Operators receive clear references regarding which components must be used, thereby reducing the risk of selecting incorrect SKUs or quantities.
Bill of Materials Examples (Single-Level and Multi-Level Structures)
A BOM structure can be simple or multi-layered, depending on the complexity of the product being manufactured. To understand this easily, consider the following examples.
1. Single-Level BOM
Imagine a company named Maju Furniture that produces simple office desks. One day, the production department receives an order for 100 desks from a customer.
Before production begins, the planner opens the BOM to view the required materials. Because the desk has no subassemblies that need to be put together separately, all material requirements are listed directly under the final product.
Product A: Office Desk
Tabletop: 1 PC
Desk Legs: 4 PCS
Brackets: 4 PCS
Bolts: 16 PCS
From this BOM, the planner can calculate the total requirements for 100 desks:
Tabletops: 100 PCS
Desk Legs: 400 PCS
Brackets: 400 PCS
Bolts: 1,600 PCS
This structure is called a Single-Level BOM because it only shows the direct relationship between finished goods and the components used. The planner does not need to navigate through additional sub-structures to determine component requirements.
A Single-Level BOM is best suited for straightforward products that do not contain subassemblies or multi-stage assembly processes.
2. Multi-Level BOM
Now, imagine the same company receives an order for 100 office desks equipped with an additional feature: a drawer unit.
To make this desk, the production team doesn't just need tabletops and desk legs. They must also construct the drawer unit first. The drawer unit consists of several materials, such as wooden panels, drawer slides, handles, and screws.
In this scenario, viewing a list of direct materials for the desk is not enough. The planner needs a multi-tiered BOM structure.
Product A: Office Desk with Drawer
Level 1
Tabletop: 1 PC
Desk Legs: 4 PCS
Drawer Unit: 1 SET
Packaging: 1 PC
Level 2 – Drawer Unit
Wooden Panels: 1 SET
Drawer Slides: 2 PCS
Handle: 1 PC
Screws: 8 PCS
When a production order is generated for 100 desks, the system calculates material requirements based on this hierarchical structure.
First-level requirements:
Tabletops: 100 PCS
Desk Legs: 400 PCS
Drawer Units: 100 SETS
Packaging: 100 PCS
However, the system must also compute the materials needed to assemble the 100 drawer sets:
Wooden Panels: 100 SETS
Drawer Slides: 200 PCS
Handles: 100 PCS
Screws: 800 PCS
This layout is called a Multi-Level BOM because the finished product contains a subassembly, the drawer unit which in turn has its own list of raw materials.
In this scenario, the purchasing department can use the BOM calculation results to procure wooden panels, drawer slides, handles, and screws. The warehouse team can prepare materials according to real demand, and production workers can assemble the drawer units before attaching them to the desk frame.
A Multi-Level BOM offers a complete breakdown of relationships between finished goods, subassemblies, and raw materials. This structure is essential for companies producing goods with multi-tier assembly operations or components built in distinct stages.
Functions of a Bill of Materials
A BOM is not used solely by production teams. The exact same data supports multiple processes across supply chain operations and manufacturing.
1. Calculating Material Requirements
A BOM calculates required raw materials and components based on total production quantity. This information helps companies ensure material availability before starting manufacturing.
2. Supporting Production Planning and MRP
Production planners use BOMs to evaluate material needs for every production order. Material Requirements Planning (MRP) systems then perform a "BOM explosion" to determine component demands relative to finished goods targets.
3. Supporting Purchasing
When calculations indicate insufficient inventory, procurement teams can plan purchases based on the required quantities and exact production schedules.
4. Supporting Warehouse Operations
Warehouses rely on BOM requirements to stage raw materials appropriately. Items can be picked or transferred to production staging areas according to active production orders.
5. Controlling Material Usage
A BOM acts as a baseline benchmark comparing expected material consumption against actual usage during manufacturing. This comparison allows businesses to identify waste, scrap, or production variances.
6. Estimating Production Costs
Material specifications and quantities in a BOM form the foundation for manufacturing cost accounting. Price changes or component modifications directly impact estimated product costs.
7. Maintaining Production Consistency
A BOM provides a standardized material specification for manufacturing products. Operators follow consistent material guidelines, leading to higher product quality and output consistency.
8. Supporting Traceability and Product Revision
When a BOM is tied to batch numbers, serial numbers, and production orders, companies can trace specific materials used in finished products. BOM Versioning also controls engineering changes, preventing production orders from using obsolete formulas or components.
Types of Bills of Materials
Bills of Materials serve different roles depending on engineering phases, manufacturing stages, and organizational needs.
1. Engineering Bill of Materials (EBOM)
An Engineering BOM (EBOM) defines product structures based on engineering designs, technical specifications, CAD drawings, or initial product blueprints. The EBOM details the technical components required to construct a product according to design standards.
2. Manufacturing Bill of Materials (MBOM)
A Manufacturing BOM (MBOM) lists materials and components actually utilized in assembly and production lines. An MBOM includes packaging materials, consumables, and hardware required for smooth shop-floor operations.
3. Sales Bill of Materials (SBOM)
A Sales BOM (SBOM) is used when multiple distinct items are sold together as a single product bundle or kit. Customers see one umbrella item, while order management systems break it down into individual components for fulfillment.
4. Configurable BOM
A Configurable BOM is utilized for highly customizable products featuring options such as dimensions, colors, capacities, features, or custom configurations. Component structures dynamically update based on customer specifications or order details.
5. Production BOM
A Production BOM serves as the active operational reference on the shop floor. It is used to generate production orders, calculate material needs, and issue raw materials from the warehouse.
What Is a Bill of Materials (BOM) Explosion?
A BOM Explosion is the process of breaking down demand for finished goods into all constituent materials and subcomponents according to the Bill of Materials structure.
For example, PT Maju Jaya receives an order for 500 units of Product A. Product A is not made from a single material; each unit requires 2 units of Component B and 3 units of Component C.
Meanwhile, Component B must be pre-assembled from 4 units of Material D and 1 unit of Material E.
When a production planner enters an order for 500 units of Product A into the software, a BOM Explosion automatically calculates total component requirements.
To produce 500 units of Product A, the company needs:
Component B: 1,000 units
Component C: 1,500 units
Material D: 4,000 units
Material E: 1,000 units
Based on these calculations, the planner knows the warehouse must stage 1,000 units of Component B and 1,500 units of Component C. Purchasing teams can verify stock availability for 4,000 units of Material D and 1,000 units of Material E, raising purchase requisitions if inventory levels fall short before production begins.
Without automated BOM Explosion, planners would have to manually compute requirements for every sub-level component. Manual calculations grow increasingly difficult and error-prone as product assembly levels increase, elevating risks of miscalculations, material shortages, or over-purchasing.
Best Practices for Managing a Bill of Materials
Use unique SKU codes and standardized naming conventions for every raw material, component, subassembly, and finished good. Avoid duplicate material entries caused by inconsistent naming formats.
Establish clear authorization workflows for creating or updating BOMs. Every change should go through a formal review and approval process to keep manufacturing structures controlled.
Implement BOM versioning and effective dates to record revisions, ensuring production orders always run with up-to-date, valid specifications.
Integrate BOM systems with inventory control, procurement, production planning, MES, and WMS software. Regularly compare standard material usage against actual consumption to evaluate variances and refine process accuracy.
How Bills of Materials Work in Modern Production Systems
In modern enterprise platforms like Warehouse Management Systems (WMS) or Transportation Management Systems (TMS), the process is automated across several key workflow steps:
1. Creating Product Master Data
The enterprise registers finished goods alongside SKUs, product names, units of measure, categories, and other master attributes so systems recognize the product.
2. Building the BOM Structure
Raw materials, components, and subassemblies are assigned to the BOM, complete with target quantities and corresponding units of measure.
3. Assigning the Active BOM Version
If a product has multiple design versions, the company assigns the active BOM version based on effective start dates, product revisions, customer profiles, or specific production needs.
4. Developing the Production Plan
Planners establish target products, output quantities, completion timelines, production lines, and machinery allocations according to business demand and plant capacity.
5. Executing Automated BOM Explosion
The system multiplies single-unit material quantities in the BOM by planned order volumes, instantly calculating total component requirements.
6. Checking Material Inventory
Exploded material requirements are cross-referenced with available inventory levels to flag sufficient stock, shortages, or needed allocations before releasing production orders.
7. Generating Material Requirements
If inventory is insufficient, the system triggers material requests for purchasing, replenishment, or internal transfers based on defined business workflows.
8. Issuing Production Orders
Once material planning is finalized, production orders are formally issued based on finished goods specifications, quantities, BOM revisions, routings, and master schedules.
9. Kitting and Material Preparation
Warehouse teams receive material pick lists derived from active production orders. Warehouse operators pick raw materials from storage locations and transport them to staging or shop-floor areas.
10. Tracking Material Consumption
During manufacturing operations, issued materials are recorded as actual consumption and measured against standard quantities defined in the BOM.
11. Recording Finished Goods and WIP
Upon completion of production stages, systems log output quantities as finished goods or Work in Process (WIP) corresponding to finished operational steps.
12. Reconciling Standard vs. Actual Usage
Companies reconcile standard BOM requirements against actual material usage to analyze scrap, defect rates, operational errors, or evolving production needs.
Managing Bills of Materials with Prieds
Prieds empowers enterprises to connect production requirements directly to shop-floor and warehouse workflows through the Prieds Manufacturing Execution System (MES) and the Prieds Warehouse Management System (WMS).
Bills of Materials serve as the baseline for production order requirements, ensuring teams know exactly which raw materials and quantities must be prepped for each run.
Prieds WMS streamlines material requests, raw material picking, inventory movements, and Material Usage logs to accurately deduct raw material inventory as consumption occurs on the floor.
Once operations produce completed items, intermediate outputs like Work in Process or final Finished Goods are posted back into stock inventory through Stock Entry and Putaway routines.
Meanwhile, Prieds MES enables companies to seamlessly track production orders, operational steps, machine runtime, operator allocations, material usage, yield outputs, and overall job progress.
Consult your business needs with the team of experts at Prieds to discover the ideal solutions tailored to your enterprise.
