Bill of materials
A bill of materials (BOM) is a structured list of every component, part and quantity needed to build one product or assembly, such as a wall panel or a module.
A bill of materials (BOM) is a structured list of every component, part and quantity needed to build one product or assembly, such as a wall panel or a module.
What bill of materials means
A bill of materials, or BOM, lists the parts that go into a defined item: part number or description, quantity per unit, and often material grade, finish and supplier. It is hierarchical, so a panel BOM may contain sub-assemblies, which in turn list screws, track, studs and boards.
Manufacturers and offsite builders rely on BOMs because production, purchasing and cost all hang off one authoritative list.
A plain example
A framed wall panel might list studs, top and bottom track, fasteners, sheathing board and a gasket, each with a quantity per panel. Multiply by the number of panels and the BOM rolls up into a purchase list. The items here illustrate structure only; a real BOM comes from the project design.
Why it matters
A clean BOM reduces ordering errors, supports accurate costing and lets a factory plan stock against the schedule. When the design changes, the BOM must be revised under version control, or the shop buys and cuts to an outdated list.
Common confusion
People swap BOM and BoQ. The bill of quantities prices project work items for a tender; a BOM defines what one assembly is made of. A material takeoff measures materials from drawings and may feed a BOM, but it is not itself a product structure.
Practical checklist
A usable BOM has a few features worth checking before production or purchasing starts.
- Each line has a unique identifier, a description and a unit of measure.
- Quantities are per one parent item, not for the whole project, so roll-ups are traceable.
- Revision number and date appear on every issue, with a record of what changed.
- Substitutions are approved and recorded, not made silently at the purchasing desk.
- Sub-assemblies are shown as levels so the structure of the product is visible.
Related terms
Questions people ask
What is the difference between a BOM and a BoQ?
A BOM lists the components of a product or assembly. A BoQ lists measured work items for a project so bidders can price them.
Who owns the BOM on an offsite project?
Typically the manufacturer or its design team, based on the approved design. Agree this in the contract.
Does a BOM include labour?
Normally it lists materials and parts only. Labour and processes usually sit in routings or the cost estimate.
Sources and further reading
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