Step-by-Step Guide to Make a Bill of Materials (BOM)

A perfect Bill of Materials (BOM) is made by listing every component and sub-assembly, giving each part the correct internal and manufacturer part number, writing exact quantities and units, adding approved alternates, and locking the list with revision control so every team member works from the same version. When these steps are done right, the BOM stays clear, complete, and ready for quoting, buying, and production.

A good BOM is a simple parts list that shows exactly what to buy and what to build. But one wrong part number, missing quantity, or unclear entry can cause a wrong quote, a wrong purchase, or a stalled build. So, how do you make a bill of materials perfectly? This guide walks you through a clear step-by-step process, shows the fields you must include, and explains how CalcuQuote BOM Health helps keep your BOM source-ready from the first quote to the final build. 

Key Takeaways

• A BOM stays accurate only when part numbers, quantities, units, and revisions stay consistent across engineering, purchasing, and manufacturing.
• The most common BOM errors are missing MPNs, wrong quantities, duplicate parts, unclear descriptions, and old revisions still floating around.
• EBOM documents what engineering designed, while MBOM reflects how the factory will build, kit, and ship the product.
• Adding AML and AVL keeps sourcing moving when a preferred part is unavailable and reduces risky last-minute substitutions.
• For PCBAs, reference designators, package/footprint, and clear DNP/DNI rules prevent wrong placement and wrong variant builds.
• A simple BOM scrub before RFQ catches issues early, before they turn into quote changes, expedite fees, or line stops.
• CalcuQuote BOM Health helps teams spot part risk early, including lifecycle changes, stock issues, long lead times, and weak supplier coverage, so teams can act before RFQ or purchasing.

How Do You Make a Bill of Materials (BOM) Perfectly?

A perfect BOM is complete, accurate, and up to date. It includes every part required for production along with part numbers, descriptions, quantities, supplier data, alternates, pricing, lifecycle status, and revision codes. The BOM must match CAD files and assembly drawings. Before sending it to production, review all fields for errors, missing entries, or inconsistencies. This removes confusion for sourcing teams and prevents expensive rework during assembly. The practices involve:

• Include every component and sub-assembly.
• Use accurate part numbers and clear descriptions.
• Note exact quantities and units.
• Apply reference designators for PCBAs.
• Add supplier details and approved alternates.
• Record pricing, lead time, and MOQ.
• Check the lifecycle status for each part.
• Mark the correct revision code.
• Match the BOM against CAD files and supplier data.

What Is a Bill of Materials (BOM) and Why Is It Important?

A BOM is the main document that describes every component required to manufacture a product. It includes raw materials, electronics components, mechanical parts, consumables, and packaging items. In electronics, it also includes ICs, passives, connectors, sockets, sensors, PCBs, and more. Factories rely on BOMs for purchasing, costing, and assembly.

Why BOMs Matter:

• Sourcing teams know exactly which components to order.
• Assembly teams get clarity on how each part fits in the build.
• Costing teams receive accurate data for reliable quotations.
• Production teams avoid errors because instructions stay consistent.

Types of BOMs You Can Create

Different types of BOMs support different stages of a product’s development. Each format plays a unique role and helps different teams stay aligned.

Engineering BOM (EBOM)

An Engineering BOM is created during the design stage. It reflects the exact components used in the schematic or CAD file. Because it is still part of the design process, it may contain trial parts, temporary components, or items that will later be replaced with production-ready versions. This BOM changes often until the design becomes stable and ready for manufacturing.

Manufacturing BOM (MBOM)

A Manufacturing BOM is the version used directly by the factory. It removes all experimental parts and lists only confirmed, production-ready components. This BOM includes complete information such as reference designators, supplier details, alternates, packaging format, and any other data the production team needs. An MBOM remains stable and supports smooth and predictable assembly.

Sales BOM

A Sales BOM is used by sales teams to describe product bundles or kits. It lists everything included in a package that customers will receive. It does not guide production but helps prepare accurate sales quotations and explains the contents of a bundled product clearly.

Service BOM

A Service BOM is created for repair and maintenance work. It includes only the parts needed to fix or service a product after it has been delivered to customers. This helps service staff quickly identify the correct replacement components without searching through the full manufacturing list.

Table: Quick Comparison of BOM Types

Here is a quick side-by-side view of the main BOM types, helping teams understand how each version supports design, manufacturing, sales, and service activities:

Core Elements Every BOM Must Include

A BOM stays useful only when it includes all key details that support purchasing, costing, and production. Here are the core components of a good BOM:

• Line Item Number: Each part receives a unique position in the list, allowing teams to reference components quickly and accurately.
• Part Number: Every component is identified by a unique code that matches the manufacturer or internal system, reducing the chance of sourcing errors.
• Description: Clear wording describes what the part is, helping teams understand it instantly without searching for additional information.
• Quantity Per Unit: This field shows how many units of a component are required for one product, keeping buying plans aligned with the design.
• Reference Designators (For PCBAs): These labels point to the exact PCB position of each component and support precise placement during assembly.
• Approved Manufacturers (AML): Multiple qualified brands are listed here, giving buyers flexible sourcing choices and reducing delays when one brand faces shortages.
• Approved Suppliers (ASL): Supplier information in this field shows where each part can be purchased, enabling purchasing teams to place orders faster.
• Pricing and Lead Time: Cost and delivery timing appear in this section, giving teams the visibility needed for accurate planning and quotation work.
• Lifecycle Status: This field shows whether a part is Active, NRND, or Obsolete, helping teams avoid components that may become unavailable soon.
• Revision Code: The current BOM version is marked here, ensuring all teams follow the same updated list during production.

Step-by-Step Process to Make a Bill of Materials (BOM)

A correct BOM follows a clear sequence that moves from choosing the BOM type to validating every detail. Use these nine steps to answer how to make a bill of materials, with correct structure, clear part identity, sourcing details, and revision control. 

Step 1: Choose the BOM type your team will use

Name the BOM view first. Use EBOM for design (PTC), MBOM for how the factory builds (Siemens Digital Industries Software), and SBOM for service parts (PTC). This stops teams from using different lists and arguing over versions.

Step 2: Decide BOM Structure: Single-Level or multi-Level

Choose a structure to match the assembly. A single-level BOM is a flat list for simple products. A multi-level BOM groups parts into subassemblies such as PCBA, enclosure, cables, and packaging, clearly showing quantities.

Step 3: Set Part Identity Rules Before You Fill Rows

Set identity rules before adding rows. Use your internal part number as the stable key, add the manufacturer part number for purchasing, write plain descriptions, and keep units consistent across the BOM.

Step 4: Fill the Core BOM Fields

Fill the core fields next: line item, level, internal part number, description, quantity, unit, revision, and short notes. These columns prevent duplicates and help reviews move fast across engineering, purchasing, and manufacturing.

Table: Core BOM columns

Step 5: Add Sourcing Fields that Remove Back-and-Forth

Add sourcing details so buyers do not chase engineering. Include manufacturer, MPN, supplier name, supplier part number, lead time if tracked, and lifecycle status. This cuts RFQ delays and reduces risky substitutions.

Step 6: Add Alternates in the Right Way (AML and AVL)

List approved alternates using AML and AVL. AML records approved manufacturer options for a part, and AVL records approved suppliers. Rank alternates so sourcing stays consistent when your first-choice item is unavailable.

Step 7: Electronics BOM Rules

For PCBAs, include reference designators, package, DNP or DNI, and variant fields. These tie each BOM line to the schematic and assembly, prevent footprint surprises, and make variant builds repeatable.

Table: Electronics-only BOM columns

Step 8: Validate and Scrub Before You Release

Fix issues before the RFQ so production does not stop later, and simplify your supply chain with smart BOM Import by letting the system structure and clean your BOM automatically.

Table: BOM validation checklist

Step 9: Control Changes With ECO to Keep the BOM Stable

Control changes with ECO. Do not edit a released BOM in place. Create a new revision, record what changed and why, set when it takes effect, and keep approvals for traceability.

What a Perfect BOM Looks Like? | Sample Table

A clean BOM uses consistent fields, clear descriptions, correct quantities, and proper sourcing details. This example shows a simple, readable format suitable for electronics products. Below is a sample table, you need to understand:

Table A:

Table A shows how the product is built. Table B shows how each line is sourced, costed, and risk-checked. Match them using the Internal PN.

Table B:

How BOM Quality Impacts Quoting, Buying, and Production?

BOM quality matters because the BOM is the single source that tells teams what to buy, how much to buy, and what to build. If the BOM is wrong or unclear, every downstream step inherits the mistake, from quoting to purchasing to production. Here’s what poor BOM quality usually causes:

• Wrong quotes: If parts, quantities, or alternates are unclear, RFQs go out with errors. You get pricing that does not match what you will actually build.
• Wrong buys: A vague description or incorrect manufacturer part number can lead to ordering a similar-looking part that does not fit, does not meet spec, or fails compliance.
• Stalled production: One missing line item or wrong quantity is enough to stop an entire build, especially in electronics, where a single component shortage can block assembly.
• Rework and scrap: A footprint mismatch, wrong package size, or wrong revision can force rework, board scrap, or last-minute substitutions.
• Variant mistakes: Without clear DNP/DNI and variant rules, manufacturers may populate parts that should not be installed or skip parts that are required.
• Audit and quality gaps: If revisions, approvals, and change records are missing, it becomes hard to prove what was built, when it changed, and why.

In short, BOM Insights enables you to combine supplier and internal data to fill BOM gaps, and a clean BOM reduces avoidable questions, prevents preventable mistakes, and keeps quoting and builds predictability. 

Where Does CalcuQuote BOM Health Fits in Your BOM Process?

CalcuQuote BOM Health helps teams keep their BOM stable by checking every line against real supply data. Instead of relying on a static spreadsheet, it shows availability, lifecycle position, pricing signals, and alternatives so teams can act early and avoid delays during quoting, buying, and production.

Here is what BOM Health adds to your process:

• Highlight incorrect or incomplete part numbers before they reach RFQ.
• Flags lifecycle risks such as NRND (Not Recommended for New Designs) or obsolete parts.
• Suggests alternative manufacturer options when the primary one is weak.
• Pulls real-time availability, pricing, and supports sourcing from 24,000+ suppliers.
• Confirms if the BOM is truly source-ready, not just formatted neatly.
• Enhances the RFQ process by aligning suppliers, reducing errors, and accelerating quote turnaround.
• Syncs with the Material Supply Planner to show parts that may delay builds.
• Helps planners understand which assemblies are safe to start and which need attention.
• Reduces rework and sourcing confusion by keeping all teams aligned on the same data.

In simple terms, BOM Health protects the BOM from hidden risks and keeps it stable from the first quote until the final build.

Ready to Build a Quote-Ready BOM

A BOM is only “accurate” if it stays usable in the real world, not only in a file. Parts go out of stock, lead times change, and lifecycle status shifts, which can turn a clean-looking BOM into a sourcing problem overnight. 

CalcuQuote helps prevent that by keeping supplier data close to your BOM, so teams can verify pricing and availability early, spot risky line items with BOM Health, and move to approved alternates before production gets blocked. It also reduces RFQ delays by keeping supplier responses and clarifications in one place, so engineering, purchasing, and program teams stay aligned from quote to buy.

Book a demo session to see how BOM Health flags lifecycle risks and checks availability across 24,000+ suppliers before you quote.

Frequently Asked Questions (FAQs)

1) How do you make a bill of materials?

To make a Bill of Materials (BOM), list every part and subassembly, assign an internal part number, add the manufacturer part number, set the quantity and unit, include approved alternates, and control revisions so everyone uses the same BOM.

2) What is the minimum information a BOM must include?

At a minimum, BOM can include part number, part description, quantity per assembly, and unit. For purchased parts, include the manufacturer name and manufacturer part number for clean sourcing.

3) How do you reduce BOM errors before RFQ or production?

Run a BOM scrub before RFQ or production by checking for missing MPNs, wrong quantities, duplicates, unclear descriptions, missing revisions, and obsolete parts. Fix issues early to avoid delays.

4) What extra fields should a PCB or PCBA BOM include?

Include reference designators (R1, C3, U7), package/footprint, and DNP/DNI rules for variants, so the assembler places the correct parts in the correct locations.

5) What is BOM Health, and how does it help?

CalcuQuote BOM Health checks each BOM line for supply risk signals like lifecycle status, stock levels, lead time, and supplier coverage, so teams can switch to approved alternates before RFQ, buying, or production.