Where-Used List
Definition
A where-used list is a report showing every parent assembly and product in which a given component appears, tracing the bill of material upward — the reverse of a BOM explosion.
In Practice
Where-used is the impact-analysis tool of BOM management. When a supplier discontinues a resistor, quality quarantines a lot, or engineering proposes a substitution, the where-used report answers "what does this touch?" — a single-level version shows immediate parents, while an indented where-used walks all the way to every affected end product.
The applications are daily: engineering change control (which products need revised documentation), recall scoping (which serial numbers contain the suspect lot, when combined with traceability records), obsolescence management (how big is the lifetime-buy exposure), and cost analysis (which products a component price increase hits). It is generated from the same single-level parent-child links as the BOM, just traversed upward.
Frequently Asked Questions
What is a where-used list used for?
Impact analysis: scoping an engineering change, finding every product exposed to a discontinued or defective component, sizing a lifetime buy, and assessing which product costs move when a part's price changes. Any decision about a component starts with knowing every structure it lives in.
What is the difference between single-level and indented where-used?
Single-level where-used shows only the immediate parents that directly consume the component. Indented where-used continues upward through each parent's parents to every top-level product affected — essential when the component sits several levels deep and the real question is which finished goods are exposed.
Related Terms
A single-level bill of material lists only an item's immediate components — one level down — with quantities per parent, serving as the building block from which multilevel product structures are assembled.
Indented Bill of MaterialAn indented bill of material is a multilevel BOM display that shows the product structure hierarchically, indenting each level so parents, subassemblies, and components appear in their true structural relationships.
Low-Level CodeA low-level code is a number assigned to each item identifying the lowest level at which it appears in any bill of material, used by MRP to ensure an item's requirements are fully accumulated before its needs are calculated.
Lifetime BuyA lifetime buy (last-time buy or end-of-life buy) is a single final purchase of a component that is being discontinued, sized to cover all expected demand — production, service, and warranty — for the remaining life of the products that use it.