Bill of materials example: a real BOM, line by line
A complete worked BOM example for a manufactured product — components, part numbers, quantities, costs, and the roll-up — plus a multi-level version.
The fastest way to understand a bill of materials is to read one. Here’s a complete, realistic BOM for a simple fabricated product — a wall-mount bracket a small fab shop might sell 40 at a time.
The example: wall-mount bracket (ASM-0042)
| Component | Part # | Qty/unit | Unit cost | Line cost | Vendor |
|---|---|---|---|---|---|
| Steel plate 6″×8″, 3/8″ | PRT-0113 | 1 | $14.20 | $14.20 | Calder Steel |
| Hex bolt M8 × 30 | PRT-0341 | 4 | $0.35 | $1.40 | Bexley Tool Co. |
| Washer M8 | PRT-0342 | 4 | $0.06 | $0.24 | Bexley Tool Co. |
| Powder coat, black | SVC-0027 | 1 | $6.00 | $6.00 | Foundry & Co (outsourced) |
| MIG wire (consumed) | CON-0088 | 0.1 lb | $2.10/lb | $0.21 | Foundry & Co |
| Material cost per unit | $22.05 |
Five things worth noticing:
- Every line has a part number — even the outsourced powder coat gets
SVC-0027, because services get reordered too. - Quantity is per finished unit, so a 40-unit build is pure multiplication: 40 plates, 160 bolts, $882 in material.
- Consumables are on the BOM. The 0.1 lb of MIG wire looks petty until you notice it’s a 1% margin leak on every job that skips it — and wire is the tame example.
- The roll-up is the quote’s floor. $22.05 is what the product costs before labor and overhead. A price below material-plus-labor isn’t a strategy; it’s a donation.
- Vendors ride along, so a shortage is one call, not a search.
The multi-level version
Suppose the bracket becomes part of a bigger product — a wall-mount workstation:
Workstation (ASM-0100) qty
├── Wall-Mount Bracket (ASM-0042) ×2 ← the BOM above, nested
├── Bench Top, laminated ×1
├── Frame Assembly (ASM-0101) ×1
│ ├── Tube 2×2, 60″ ×4
│ └── Foot, adjustable ×4
└── Hardware kit ×1Each assembly keeps its own BOM; the parent references it as one line. Costs roll up the tree (the workstation inherits 2 × $22.05 from the brackets) and demand explodes down it (10 workstations → 20 brackets → 20 plates, 80 bolts). This is exactly the computation MRP automates — and exactly where hand-maintained spreadsheets start silently lying after the first revision.
Build your own
Start with the free BOM template — its columns match this example. When the BOMs need to know your live stock (“can we build 40 today?”), that’s BOM software’s job: same structure, connected to the shelf.