Definition
A bill of materials (BOM) is a structured list of all parts, materials and quantities required to manufacture a product, often organized hierarchically to describe how components fit together.
How it works
A BOM is organized by assembly level: the finished product breaks down into subassemblies, which break down further into individual parts, with each line recording fields such as name, specification and quantity. It underpins purchasing, inventory and production scheduling, and must be updated when designs change.
Usage
BOMs are common in hardware manufacturing, electronics design and open-source hardware projects; DIY builders sharing a build or a custom device also attach a parts list.
Related and confusable terms
A BOM answers “what materials are needed” and complements assembly instructions, which answer “how to build it”. In do it yourself (DIY) projects, the BOM often appears as the companion checklist to a tutorial.