A bill of materials is a list that specifies the parts used to build a product. When a company produces a product, it must keep track of the materials and components used in its creation. This bill of materials must be included with the product before shipping it to a merchandiser, client, or buyer. Generally, it is included inside the box in which the product is shipped.

In a way, a bill of materials is similar to a recipe. Every ingredient used is listed in the bill of materials. Strict record keeping is the key rule to creating a bill of materials, because no item can be skipped. This is largely because the bill of materials can be used later to narrow down issues for repairs of a product if necessary. In addition, a bill of materials is essential when ordering replacement parts.

For an idea of what information is listed on a bill of materials, it is helpful to look at a sample bill of materials for a chest freezer. The chest freezer's components are broken into three parts: door, cabinet, and system. Each of these parts also contains a list of materials.

For the door, the bill of materials includes a white door gasket, lock assembly, key lock, inner lid panel, outer door panel, plug button, screw washers, panel clips, and insulation. Though this may mean little to a layperson, someone with knowledge of appliances can quickly identify problems and find replacement parts if or when the time comes by looking at the bill of materials. The freezer's cabinet is next on the bill of materials. The cabinet's list contains breaker ends, frame, nameplate, temperature control knob, temperature control gauge, screw hinges, breaker corners, hinge assemblies, breaker hinge, screws, owners manual, parts list, touch-up paint, bill of materials sheet, and the panel access.

Finally, there is a bill of materials for the freezer's system. The system's bill of materials includes the condenser, drier, filter, electrical harness, clip springs, screws, washer heads, grommets, compressor, compressor electricals, starter, overload protector, wiring harness, compressor cover, ground wires, fasteners, and energy guide. Even the screws are listed separately by size on a bill of materials, which makes it easier for someone performing repairs to find the exact replacement screw needed.