Ask a manufacturer "how much raw material do you need to make 100 units?" and the answer tells you everything about how well their factory is run.

If the answer is "let me check my register" or "it depends on the operator," production planning is happening in someone's head — and inventory, cost, and delivery accuracy all suffer as a result.

The solution starts with a Bill of Materials.

What Is a Bill of Materials?

A Bill of Materials (BOM) is a structured list of every raw material, component, sub-assembly, and quantity required to manufacture one unit of a finished product.

Think of it as the recipe for your factory. Just as a recipe tells a chef exactly what ingredients and quantities produce a dish, a BOM tells your factory exactly what inputs produce one unit of output.

A simple BOM for a cotton T-shirt would list: cotton fabric (30s) at 1.8 metres per shirt, polyester thread at 150 metres, one brand label, one size label, three buttons, and one packaging polybag. Every production order for that T-shirt consumes exactly these materials in these quantities — unless you update the BOM.

Why Your Factory Needs a BOM

Without a BOM, three things break.

Inventory deductions are guesswork. When production completes, someone has to decide how much raw material to deduct from stock. Without a BOM, this is based on memory, habit, or nothing at all. Within weeks, your system inventory doesn't match your physical stock.

Procurement planning is reactive. If you don't know exactly what goes into each product, you can't plan purchases in advance. You buy when stock runs out, not before. Rush purchases, premium freight costs, and production stoppages follow.

Cost per unit is wrong. Material cost is typically 60–80% of a manufacturer's total cost. If you don't know exactly what materials go into each unit, your cost per unit is an estimate. Pricing decisions made on wrong cost data erode margins without you knowing it.

Types of BOMs

Single-Level BOM

Lists the direct components of a finished product. Suitable for simple products with no sub-assemblies. A cotton bag BOM might contain cotton canvas (0.5 metres), cotton rope (1.2 metres), two metal eyelets, and one label.

Multi-Level BOM

Used when your finished product contains sub-assemblies that are themselves made from components. An assembled motor pump would have a pump casing, an impeller, a seal kit, and a motor sub-assembly — where the motor sub-assembly itself breaks down into a housing, copper winding, bearings, and a shaft.

Auto component, electronics, and engineering manufacturers typically need multi-level BOMs.

Engineering BOM vs. Manufacturing BOM

The Engineering BOM (EBOM) is designed by the engineering team and describes how a product is designed. The Manufacturing BOM (MBOM) is used by the factory floor and describes how the product is actually made — including consumables, packaging, and tooling not in the EBOM.

For most Indian MSMEs, you need a Manufacturing BOM.

How to Build a BOM: Step by Step

Step 1: Pick one finished product to start. Don't try to BOM everything at once. Pick your highest-volume product or your most complex one.

Step 2: Walk the production floor. Don't build the BOM from memory or estimates. Walk through the actual production process with your production supervisor. At each stage, note what material or component is consumed, how much per unit (weighed, counted, measured), and whether there's standard wastage to account for.

Step 3: Record standard quantities with wastage. A BOM should reflect actual consumption, not ideal consumption. If your process always wastes 5% of fabric due to cutting, the BOM should include 1.05 metres per unit for a process that theoretically needs 1 metre. Build the wastage in — don't pretend it doesn't exist.

Step 4: Add packaging materials. Manufacturers often forget packaging in their BOM. Boxes, polybags, labels, stickers, bubble wrap — all of these are real costs and should be tracked.

Step 5: Assign the correct unit of measure. Use the unit you actually purchase and consume in. Fabric in metres or kilograms, liquids in litres or millilitres, hardware in pieces, wire in metres or kilograms. Mixing units (buying in kg but tracking in pieces) causes reconciliation headaches.

Step 6: Enter into your manufacturing system. A BOM only delivers its value when it's in a system that uses it to auto-deduct inventory on production completion, calculate material requirements for planned production, and generate purchase requirements when stock falls below reorder levels. A BOM in a spreadsheet is better than nothing. A BOM in a connected manufacturing system is operationally transformative.

BOM and Material Requirements Planning (MRP)

Once your BOMs are set up, Material Requirements Planning (MRP) becomes possible. MRP takes your production plan — X units of product A and Y units of product B over the next four weeks — and calculates exactly what materials you need to order and when.

Without BOMs, MRP is impossible. With BOMs, your procurement team gets a system-generated purchase plan instead of relying on gut feel.

Common BOM Mistakes

Using theoretical quantities instead of actual ones. If your BOM says 1.00 m of fabric but actual usage is 1.05 m, your inventory will go negative within weeks.

Not including consumables. Tape, thread, solvents, polybags — small items that aren't tracked will slowly drain inventory accuracy.

Never updating the BOM. When you change a component, switch a supplier, or redesign a product, the BOM must be updated. An outdated BOM is worse than no BOM — it gives you false confidence.

One BOM for multiple product variants. If you make a T-shirt in 5 sizes with slightly different material consumption per size, you need 5 BOMs. Don't average it.

BOM in FactoStack

In FactoStack's production module, you can create multi-level BOMs per product, set standard quantities with wastage percentages, attach the BOM to a production order, and auto-deduct raw materials from inventory when production is marked complete. When a production order is raised, the system uses the BOM to check current stock levels and flag any shortages before production starts — eliminating last-minute material surprises.

Production Planning & BOM Management

Set up multi-level BOMs, auto-deduct raw materials on production completion, and plan purchases based on live material requirements.

See how it works →Book a demo

What Is a Bill of Materials (BOM) and How to Set One Up for Your Factory