What is a bill of materials?

A small producer makes a wooden table. One table needs a top, four legs, screws and a coat of varnish. Once that is fixed, you know for ten tables exactly what to buy and what comes off the stock.

A list can have several levels. A part you make yourself, a semi-finished product, then has its own list with its own raw materials. That way a product is built from parts that are themselves made from parts. Each part has its own item number, so it can be found without doubt.

What goes wrong without one? Someone estimates the quantities from memory, and stock runs out at the wrong moment. Or a product is made in two variants but the list fits only one. The cost price also becomes unreliable if the list lags behind what is really used.

Make sure the list matches practice. If the shop floor uses a different part from the one on paper, the list needs updating. Keep one person responsible for changes. Anyone who wants to plan from the list ends up at MRP, the calculation of what to buy or make and when.

A good list is above all an agreement: this is what goes in, and this is how we make it. So a new variant or a changed design also means an updated list, before the first order is planned. That prevents the workshop from carrying on with the old version while purchasing already orders something different. Keep the old version for reference, but make clear which one is current.