How To Make A BOM

A bill of materials is where manufacturing discipline becomes visible. Before a purchase order is raised, before a work order is released, before the shop floor asks why one small component is missing, the BOM has already decided whether production will run smoothly or get interrupted halfway.

For many small and mid-sized manufacturers, the first BOM is made in a spreadsheet. That is fine in the beginning. The trouble starts when the same spreadsheet becomes the only source of truth for purchase, stores, production, costing, quality, and dispatch. One team updates a component quantity, another team keeps using the old version, purchase orders material from memory, and finance later discovers that the quoted margin was based on an incomplete cost structure.

A good BOM is not just a list of raw materials. It is a controlled manufacturing record. It tells the business what is required, in what quantity, at what stage, with what tolerance, from which approved source, at what cost, and under which revision. When that record is connected to inventory and production through AICAN Optiwise, the BOM becomes an operating system for better planning instead of a static file.

What Is A BOM In Manufacturing?

A BOM, or bill of materials, is the structured list of materials, parts, assemblies, consumables, packaging, and sometimes operations required to make a finished product. Think of it as the product recipe, but with manufacturing controls added.

A food recipe may say two cups of flour. A manufacturing BOM needs more precision. It may need item code, item description, grade, unit of measure, quantity per finished unit, scrap allowance, alternate material, approved vendor, inspection requirement, cost, routing step, and revision number.

For example, a small electrical assembly may require:

• Sheet metal enclosure
• DIN rail
• Terminal blocks
• Wiring harness
• Labels
• Fasteners
• Packaging carton
• Final inspection checklist

If any one of these is missing from the BOM, the production plan may look achievable on paper but fail on the shop floor.

Why A BOM Matters More Than It Looks

A weak BOM creates silent losses. The loss does not always appear as one large visible failure. It appears as repeated small frictions: urgent purchases, excess stock, wrong material issues, rework, delayed dispatches, unclear costing, and margin leakage.

A strong BOM helps a manufacturer:

• Calculate material requirement from sales orders or production plans
• Avoid buying excess material just because demand is unclear
• Estimate product cost before committing to a customer price
• Maintain quality by using approved grades and specifications
• Reduce dependency on one experienced production person
• Create repeatable production even when team members change
• Track revisions when product design changes

This is why BOM accuracy is not only an engineering concern. It affects purchase, inventory, finance, sales, quality, and customer delivery.

Start With The Finished Product Code

The first step is to define the finished product clearly. Do not begin with a random component list. Begin with the product identity.

For each finished good, capture:

• Finished product name
• Unique item code
• Product category
• Unit of measure
• Drawing number or specification reference
• Customer-specific variant, if applicable
• Revision number
• Effective date

The product code matters because similar items often have small differences. A machine panel for Customer A may look almost identical to Customer B's panel, but one may use a different enclosure thickness, different wiring colour, or different label set. If both versions are handled casually under the same product name, mistakes are almost guaranteed.

Decide Whether You Need A Single-Level Or Multi-Level BOM

A single-level BOM lists all materials directly under the finished product. It works for simple products where there are no meaningful subassemblies.

A multi-level BOM breaks the product into assemblies and subassemblies. This is better when one part of the product is manufactured separately, stocked separately, inspected separately, or used across multiple finished goods.

For example:

Finished Product: Control Panel

Subassembly 1: Enclosure Assembly

Subassembly 2: Wiring Harness

Subassembly 3: Label And Packaging Kit

Each subassembly can have its own BOM. This makes planning cleaner because the same wiring harness may be used in multiple products. It also helps production teams issue material by stage instead of dumping everything at once.

A practical rule: if a group of components is made, inspected, or stocked together, consider making it a subassembly.

List Every Material, Not Only The Expensive Ones

Many BOM errors happen because teams capture expensive raw materials but ignore low-value items. Screws, labels, adhesives, sleeves, cartons, tapes, washers, and consumables may look minor individually, but they can stop dispatch just as effectively as a missing motor.

Your BOM should include:

• Raw materials
• Bought-out parts
• Semi-finished components
• In-house manufactured parts
• Consumables used per unit
• Packaging material
• Labels and inserts
• Customer-specific accessories
• Mandatory inspection or documentation items, where needed

For costing, decide whether consumables are captured per unit, per batch, or as overhead. But do not leave them invisible. Invisible costs become invisible leakage.

Define Quantity And Unit Of Measure Carefully

Quantity errors are one of the fastest ways to damage production planning. The BOM must state exactly how much of each item is required to make one finished unit.

Pay attention to unit of measure. A component may be purchased in kilograms, issued in grams, and consumed per piece. A wire may be purchased in rolls, issued in meters, and consumed in millimeters. A liquid may be bought in litres but applied in millilitres.

If units are inconsistent, purchase may order too much, stores may issue too little, and costing may become meaningless.

Use a standard rule:

• Keep one base unit for inventory
• Convert purchase and production units through approved conversion factors
• Mention quantity per finished unit clearly
• Add scrap or process loss separately instead of hiding it in the main quantity

For example, if a product needs 1.8 meters of cable and typical process loss is 3%, do not simply enter a rounded 2 meters without explanation. Capture the actual required quantity and the scrap factor. It helps both costing and continuous improvement.

Add Scrap, Wastage, And Yield Assumptions

Manufacturing is rarely perfect. Cutting, machining, printing, coating, soldering, molding, and packaging may create process loss. If that loss is real, the BOM should reflect it.

There are two common ways to handle this:

• Add a scrap percentage at component level
• Add a batch-level wastage allowance

Component-level scrap is cleaner when wastage differs by material. For example, sheet metal may have cutting loss, but bought-out fasteners may not. If both are given the same generic wastage factor, costing becomes distorted.

The important point is to make wastage visible. Once visible, it can be measured. Once measured, it can be reduced.

Capture Approved Alternatives

Factories often need alternate materials. A specific grade, vendor, or brand may not always be available. But alternatives must be controlled. If production substitutes material informally, quality and compliance risk increases.

A good BOM includes approved alternatives with conditions:

• Alternate item code
• Equivalent specification
• Approved vendor
• When it can be used
• Whether customer approval is required
• Whether cost or performance changes

This is especially important for regulated products, export orders, electrical assemblies, food-contact materials, medical components, and customer-approved drawings.

Connect BOM To Costing

A BOM should support product costing. At minimum, it should help calculate material cost per unit. Better systems also connect labour, machine time, subcontracting, overhead, scrap, and packaging.

Material cost is usually calculated as:

Component quantity x current or standard rate

But the rate method must be defined. Are you using last purchase rate, weighted average, standard cost, landed cost, or vendor quotation? Different methods give different margins.

For quote preparation, many manufacturers prefer standard or estimated cost. For accounting and stock valuation, they may use weighted average or another approved method. The key is not to mix methods casually.

Optiwise by AICAN helps manufacturers connect item masters, stock, purchase, and production records so BOM-based costing is not maintained in isolation.

Add Routing Or Process Information Where Needed

Some BOMs include only material. Some also link to routing, which means the sequence of operations required to make the product.

Routing may include:

• Cutting
• Machining
• Welding
• Assembly
• Testing
• Packing
• Outsourced process

If process cost, machine capacity, or stage-wise material issue matters, routing should be connected to the BOM. This helps the business understand not only what is required, but when and where it is required.

For example, packaging material should not be issued at the machining stage. A routing-linked BOM can prevent early issue, loss, or confusion.

Control BOM Revisions

A BOM without revision control is dangerous. Product designs change. Vendors change. Material grades change. Customer specifications change. If old and new BOMs are mixed, production may build the wrong version.

Every BOM should have:

• Revision number
• Revision date
• Reason for change
• Changed by
• Approved by
• Effective from date or order number
• Old material treatment plan

The effective date is critical. If one customer order was approved under the old specification and another under the new one, production must know which BOM applies.

Get Cross-Functional Approval

Engineering may create the BOM, but it should not approve it alone. Purchase, stores, production, quality, and finance should review the parts relevant to them.

A practical approval flow:

1. Engineering creates the first BOM.
2. Production checks manufacturability and stage-wise usage.
3. Stores checks item codes and units of measure.
4. Purchase checks vendor availability and alternates.
5. Quality checks specifications and inspection needs.
6. Finance checks cost assumptions.
7. An authorized person releases the BOM.

This may sound formal, but even a simple approval checklist can prevent expensive mistakes.

Common BOM Mistakes To Avoid

The most common mistakes are not technical. They are control mistakes.

Avoid these patterns:

• Using product names instead of unique item codes
• Mixing purchase unit and consumption unit without conversion
• Keeping old revisions active without clear status
• Leaving packaging and labels out of the BOM
• Hiding scrap inside rounded quantities
• Allowing production to substitute material without approval
• Creating duplicate item masters for the same component
• Updating spreadsheets without informing purchase and stores
• Costing from one BOM while producing from another

The fix is not only better documentation. The fix is a connected system where item master, BOM, purchase, stock, production, and costing speak to each other.

How Optiwise Helps Manufacturers Manage BOMs

AICAN Optiwise is built for manufacturers who need practical control without turning the business into a paperwork exercise. A BOM in Optiwise can become the basis for material planning, production orders, stock issue, costing, and purchase visibility.

Instead of asking teams to maintain separate Excel files, Optiwise helps create one operating record for the product. That means purchase sees what is required, stores sees what must be issued, production sees what must be consumed, and management sees the cost impact.

The real value is not that the BOM is digital. The value is that the BOM becomes usable in daily decisions.

Founder’s Note

At AICAN, we have seen many manufacturers lose money on products they believed were profitable. The reason is often not bad sales. It is an incomplete BOM, an outdated rate, an invisible consumable, or a small quantity error repeated across hundreds of units.

Our view is simple: a BOM should be easy enough for the team to maintain and strong enough for management to trust. When the product record is clean, the factory becomes calmer. Purchase plans better, production asks fewer emergency questions, and finance gets a truer picture of margin.

FAQs

What is the first step in making a BOM?

Start by defining the finished product code, specification, unit of measure, and revision. Then list the materials and subassemblies required to make one finished unit.

Should packaging material be included in the BOM?

Yes, if packaging is required for dispatch or costing. Cartons, labels, inserts, tapes, pallets, and customer-specific packaging can affect both availability and margin.

What is the difference between single-level and multi-level BOM?

A single-level BOM lists all items directly under the finished product. A multi-level BOM breaks the product into subassemblies, which is better for complex products or reusable assemblies.

How often should a BOM be updated?

Update it whenever there is a design, material, vendor, quantity, process, or packaging change. Every change should have revision control and approval.

Can Optiwise manage BOM and inventory together?

Yes. Optiwise by AICAN connects BOMs with inventory, purchase, and production records so material planning and costing are based on the same product structure.