What is a bill of materials?
A bill of materials (BOM) is the master parts list that production, procurement, and finance all build from to make one product. It exists so every team works from one source of truth instead of separate spreadsheets. That is how you avoid missing parts, wrong quantities, and costly rework. Think of it as the backbone of manufacturing, used anywhere products are built, assembled, or repaired.
Key characteristics
- What it lists: part numbers, part names, descriptions, quantities, unit of measure, and whether each item is made in-house or purchased. Getting these fields right is the core of managing your BOMs.
- BOM levels: a single-level BOM is one flat list, while a multi-level (indented) BOM maps Level 0, the finished product, down through every subassembly.
- Types of BOM: different stages of work call for different lists. The three most common:
| Type | What it captures |
|---|---|
| Engineering BOM (EBOM) | The product as designed by engineering. |
| Manufacturing BOM (MBOM) | The product as built on the floor, including packaging and consumables. |
| Configurable BOM (CBOM) | The options and rules used to build product variants. |
- Feeds planning: a BOM drives material requirements planning (MRP) and inventory control, calculating what to order and when so parts arrive in time to build.
- Accuracy matters: a BOM is only as reliable as the data inside it, and manufacturing data quality is a widespread problem.
A 2024 survey of 500 manufacturing leaders found that 98% of manufacturers struggle with data issues in their operations. Separately, Supply Chain Management Review’s 2025 Warehouse and DC Operations Survey found only 57% keep fully accurate item master data, down from 60% the year before. That leaves 43% of operators working from item records that can feed the wrong parts, quantities, or units into a BOM.
Example
A bicycle BOM lists the parts you need to build one bike. That includes one frame, two wheels, two brakes, one handlebar, and the fasteners that hold it together, each with its own part number and quantity. It also captures the assembly steps: mount the wheels, then the brakes, then the handlebar. Precise parts lists pay off: Fishbowl customer the KidWind Project reduced on-hand inventory costs from $270,000 to between $80,000 and $100,000 by managing its parts and products more precisely.
Related terms
FAQ
What is the difference between a BOM and a recipe? A BOM works like a recipe for a manufactured product, but it also tracks part numbers, quantities, units of measure, and whether each item is made in-house or purchased.
What are the main types of bill of materials? The most common are the engineering BOM (EBOM), the manufacturing BOM (MBOM), and the configurable BOM (CBOM), each built for a different stage or workflow.
Why does BOM accuracy matter? An inaccurate BOM leads to missing parts, wrong quantities, and rework, so keeping it current protects inventory accuracy and on-time production.
Ready to build cleaner lists? See how Fishbowl’s bill of materials software helps you create and manage BOMs.