what is a bill of materials

The Bill of Materials (BOM) is an essential part of the manufacturing process. It’s an overview of all the components needed to make the finished product, as well as any additional materials, such as packaging and user guides.

In this post, we’ll look at what a BOM is, why it’s important to have, the elements included in a BOM, and the questions you should ask as you’re creating a BOM.


What is a Bill of Materials?

To put it simply, a bill of materials is a document that lists all the materials required to make a built product, including the quantities, parts, subassemblies, and consumables. The BOM doesn’t typically include a rundown of where materials are used or at what point in the manufacturing process they are needed. However, it’s sometimes formatted in an ordered manner that correlates to the steps of production.

The BOM usually includes some materials that are not part of the production of the product itself such as shipping and packaging materials, user guides, and consumable items.


Why is a Bill of Materials Important?

An accurate BOM is important because without all the right information, the manufacturing process can easily be hindered or interrupted.

A BOM impacts several areas of your business. It directly affects your inventory, because when the purchase of raw materials isn’t accurate, your products may not be made and available for sale when you need them. Additionally, without correct BOM information, you can’t make sound business decisions about the cost-effectiveness of your materials.

An inaccurate BOM leads to wasted funds, inefficient production, loss of revenue, and dissatisfied customers. So, it’s important you know all the elements included in a BOM, and how they should be completed. Using a BOM not only makes the manufacturing process easier, it also makes it much easier to calculate COGS.


The Elements of a Good Bill of Material

The following are the typical components you’ll find on a quality BOM:

BOM level: This is the ranking or number that every specific part holds within the overall BOM. It makes the BOM easier to follow.

Description: Every part or material listed should have a detailed description. It will help you and others identify specific materials and distinguish between materials and parts that are similar.

Part number: Each part or material listed is assigned a unique part number. This allows anyone involved in the manufacturing process to identify materials or parts easily.

Part name: This is a detailed, unique name for each part, material, or assembly. It allows everyone in the manufacturing process to easily identify the part without having to cross-reference with other sources.

Phase: This component refers to the lifecycle stage (or status) of each part in the BOM. For example, a status like “In Production” might be used to describe a part that is in the process of being completed. Other terms, like “Unreleased” or “In Design” may be used for materials or parts that are in the approval phase.

Procurement type: This element refers to how each part is sourced.

Quantity: This item details how many of each part or material is used in each assembly for the BOM.

Reference designators:If a product includes printed circuit board assemblies (PCBAs), this field is used to explain how that part fits the circuit board.

Unit of measure: Terms like inches, feet, ounces, and other units of measure are used for each part or material.

BOM notes: This section is for any additional information necessary that isn’t contained in the other parts of the BOM.


Questions to Consider when Writing a Bill of Material

To ensure that you’ve included everything on your BOM, it’s important to ask yourself the following questions:

What is the system of management for my BOM?– What is your plan for managing the multiple revisions it will likely go through before it’s finalized? Most BOMs go through at least a few iterations as your manufacturing process evolves. You need a system in place to ensure that your team always has the most up-to-date version to work with.

Who is going to use my BOM? – Consider everyone in the manufacturing process who needs to have access to the BOM. Make sure that the information they each need is included and that they have access to the document.

Are the any consumables I need to itemize?– Sometimes consumables (for example, fasteners, glue, labels, boxes, etc.) are overlooked when the BOM is completed. Make sure that you haven’t left any mass-quantity consumables off your BOM.

Are there files that must be attached to my BOM?– Your BOM may need to have supporting documentation attached to it, like part datasheets, or other important information. Don’t forget to include them.


Final Thoughts about the Bill of Materials

Having an accurate and comprehensive BOM for products you design and have manufactured is a critical step in the manufacturing process. When you get it right, you have a road map that will serve you and your partners in the supply chain well. When you don’t, you may suffer the consequences of inefficiency and uninformed decision-making, which will definitely have a negative impact on your business.

With the information we’ve detailed above, you have the starting point to create and maintain your BOMs effectively. Let us know in the comments below if we’ve missed anything.

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