A bill of materials lists every input that goes into one unit of a finished product, with the quantity of each. It is the recipe for manufacturing.
An example: a 1.5 HP borewell submersible pumpset
| Component | Qty per pump |
|---|---|
| Pump stages and casings | 1 set |
| Stator stampings | 4.2 kg |
| Copper winding wire | 3.1 kg |
| Shaft | 1 |
| Cable | 1 set |
| Packing carton | 1 |
What a BOM is used for
- Buying
- an order for 500 pumps means 1,550 kg of copper wire, plus a margin for waste.
- Costing
- add up the inputs at current rates, plus labour and overheads, to know the true cost per pump.
- Stock
- when a pump is made, the inputs come off stock and one finished pump goes on.
- Job work
- a BOM shows what to expect back from a job worker for what was sent.
Keeping it right
A BOM drifts. Designs change, suppliers change gauges, and actual use creeps above the standard. Comparing material issued with the BOM each month shows where waste is building up. Food makers call it a recipe, garment makers a costing sheet; the idea is the same.