What is a bill of materials (BOM)?

The short answer

A bill of materials is the recipe for a product: every part, material and sub-assembly it needs, and how much of each goes into one finished unit.

What goes into a BOM

At minimum: the part name or SKU, the quantity per finished product and the unit (pieces, metres, grams). Many teams also record the supplier, the unit cost and an allowance for waste.

Single-level vs multi-level BOMs

A single-level BOM lists parts that go straight into the product. A multi-level BOM includes sub-assemblies — for example a lamp's base, which is itself built from several parts.

Multi-level BOMs let you build and stock sub-assemblies ahead of time and see exactly which ones you need to make next.

Why BOMs matter for inventory

With a BOM, recording one production run can deduct every part automatically. You can also see how many finished products you can build from current stock, and what to reorder before you run short.

Getting started

Start with your best-selling product. List every part, weigh or measure quantities rather than guessing, and add waste where it's real. Then do the same for the next product.