A bill of materials, or BOM, is a structured list of the components, materials, quantities and relationships required to make a product. It connects product design to sourcing, costing, production, quality and change control.
What does a BOM contain?
- Part numbers and descriptions
- Required quantity and unit of measure
- Revision and effective dates
- Approved manufacturers or substitutes
- Assembly level and parent-child relationship
- Notes, specifications and scrap assumptions
How is material cost calculated?
Extended component cost equals required quantity multiplied by unit cost. If a product uses four components costing $3.50 each, two components costing $8 each and one component costing $12, illustrative direct material cost is (4 × $3.50) + (2 × $8) + (1 × $12) = $42, before scrap, freight, duty and labor.
Engineering BOM vs. manufacturing BOM
An engineering BOM reflects the product as designed. A manufacturing BOM organizes everything needed to build and package it using the actual production process. The structures may differ while describing the same finished item.
How should changes be controlled?
Version the BOM, define effective dates, assess inventory and supplier impact, and require approval before production use. A quotation or purchase order should identify the applicable revision so price and quality are not evaluated against different designs.
