Bill of Materials (BOM): Components, Yield and Purchasing Example

A bill of materials (BOM) is the complete list of raw materials, components, and sub-assemblies required to produce one unit of a finished product — including quantities, units of measure, and yield adjustments — serving as the bridge between sales forecasts and procurement requirements.

Quick answers

What is a bill of materials? A BOM is a structured recipe for a finished product. It lists every input — ingredient, component, packaging — along with the exact quantity needed per unit of output. For a planned production quantity, BOM explosion calculates gross component requirements. Purchasing then accounts for usable stock, allocations, incoming supply, dates and supplier packs to determine what to buy.

What's the difference between a single-level and multi-level BOM? A single-level BOM is a flat list: Product A requires 3 of Part X, 2 of Part Y, 1 of Part Z. A multi-level BOM includes sub-assemblies: Product A requires 1 of Sub-Assembly B, which itself requires 2 of Part X and 1 of Part Y. Multi-level BOMs are common in manufacturing. In food service, a prepared sauce or dough can form a sub-recipe used by several finished dishes.

Are recipes BOMs? Yes. A restaurant recipe is a BOM. A cocktail recipe calling for 2 oz bourbon, 1 oz sweet vermouth, and 2 dashes bitters is a three-component BOM with specific quantities. The ingredient structure supports recipe costing; menu engineering also considers sales mix, pricing and contribution. An updated component price changes the material estimate when the costing basis uses that price.

What is BOM cost? Material BOM cost is the cost of the required components, accounting for the stated quantities and yield treatment. A broader product cost roll-up may add labor, operations and overhead; label the included costs. If a cake uses $10.79 of ingredients and packaging plus $6.00 of labor, the BOM cost is $16.79 per cake.

What about retail bundles? A gift set containing three products is a BOM. A kit assembled from individual components is a BOM. Any time a single sellable unit is composed of multiple procured items, a BOM defines the relationship.

BOM cost meaning and formula

BOM explosion (component demand):

Gross component requirement = Σ (planned production × usable quantity per unit / yield rate)

where:

• finished good demand — units of the finished product to be produced (from forecast or orders)
• quantity per unit — usable amount of this component required per finished good in this example
• yield rate — the fraction of the raw input that becomes usable output (e.g., 0.85 for 85% yield)

BOM costing:

Material cost per unit = Σ (usable component quantity / yield rate × component unit cost)
Illustrative product cost = Material cost + Included labor cost

BOM yield adjustment

At the assumed 70% yield, 200g purchased provides only 140g usable: 30% less usable quantity than the 200g recipe requires. State whether the BOM stores usable or raw input quantities. Apply the yield adjustment once: dividing an already adjusted raw quantity by yield again would overstate requirements.

Worked example

A bakery sells a signature cake. The BOM per cake:

These are illustrative costs and yields, not a recipe or food-safety specification. Retain full precision while aggregating demand; round the final procurement quantity to the purchasable unit. The bakery forecasts 80 cakes for next week. BOM explosion: 80 × 500g / 0.98 ≈ 40.816kg flour, 80 × 250g = 20kg butter, and 80 × 6 / 0.95 ≈ 505.263 eggs, rounded to 506 eggs before applying supplier pack sizes, and so on. These are gross component requirements. If 100 unallocated, usable eggs are on hand and 120 more are confirmed to arrive before production, the simplified shortage is 505.263 − 100 − 120 = 285.263 eggs. With 30-egg supplier packs and no additional buffer, round the purchase to 300 eggs. Confirm dates, allocations and expected loss before placing the order.

If butter price increases from $0.0088/g to $0.0110/g, the BOM recalculates: butter cost per cake rises from $2.20 to $2.75, total BOM cost rises to $17.34, and the operator can decide whether to raise the cake price, reformulate, or absorb the margin hit — with exact numbers.

Keep the BOM and purchase plan consistent

• Version and output basis: identify the approved recipe or product version, output quantity and effective date. A batch recipe for ten cakes is not a per-cake recipe.
• Units and yield: convert grams, kilograms, cases and individual units consistently. State whether quantities already include expected loss.
• Shared inputs: aggregate requirements across products and account for sub-assemblies without counting their components twice.
• Netting and dates: distinguish gross production demand from the shortage remaining after usable stock and scheduled receipts. Check that supply arrives before it is needed.
• Cost basis: identify standard, current or agreed supplier prices. Material estimates are not the same as recognized COGS or total production cost.

Microsoft’s BOM and formula documentation distinguishes the material structure from the operations and resources used to estimate product cost. The bakery arithmetic above is an educational example, not a claim that every planning system applies the same yield logic.

Evaluate the purchasing handoff

In a LineNow procurement demonstration, bring two finished goods sharing one component. Inspect the demand input, units, available stock, incoming supply and a supplier price change. Follow the resulting purchase through its supplier confirmation, partial receipt and accounting handoff.

If you require multi-level production planning, capacity scheduling or an automatic cost roll-up, demonstrate those requirements explicitly with your ERP and production records. A living purchase order carries supplier execution forward from the component plan.

Related

• Procurement Software
• Purchase Order Software
• Supplier Management Software
• Consumption Rate: Definition and How to Measure It
• Landed Cost: The True Cost of Inventory
• Economic Order Quantity (EOQ) Formula