Multi-Level BOMs Explained for Product-Making Businesses

Manufacturing businesses with a complex manufacturing process involving subassemblies will need a multi level BOM. Here we look into how to make them work.

Disassembled bike from multi-level BOM.
Published: 11.01.2021

A multi level bill of materials (BOM – sometimes referred to as an indented bill of materials) is a bill of materials that details exactly how you build your product which includes each sub assembly, components, and materials that goes into making it.

In your multi level BOM, the hierarchical BOM structures will show your finished product at the top, including your SKU’s, part descriptions, quantities, costs, and any additional specifications.

Multi level BOMs are a vital ingredient for manufacturing, especially for manufacturers who use multiple sub-assemblies to produce their finished goods.

But before we continue, there are different types of BOMs you should be aware of. The BOM structures appear as:

  1. Modular BOM;
  2. Configurable BOM; and
  3. Multi level BOM.

Centralize your multi level BOM with the Katana 14-free trial.

In this article, we’re going to go explore the world of multi level BOMs, and everything you need to know to get more control over them. But, if you think you have a pretty good grasp on them, we’d recommend skipping to the smart manufacturing software chapter.

Structure of a Multi Level BOM

The structure of a multi level BOM resembles a family tree, and maps out all components and sub assemblies for a product.

Each BOM level will detail all the components that are directly or indirectly used in the production of a parent item.

The purchased parts and raw materials can also be found within a BOM level, which will look something like a BOM tree.

Multi-level BOM.


PRO TIP: When you’re defining your multi-level BOMs it’s going to be a lot easier if you use SKU’s to track your inventory. However, if you have a huge amount of inventory, it can be difficult to come up with SKU’s. Luckily, there are SKU generators that can help you with this task.

Importance and Purpose of Multi Level BOM

If you want to get your operation set-up with the smoothest production flow possible, there’s a lot you need to do, as to not bog down your production later.

This includes finding the best manufacturing routes and optimizing your manufacturing inventory management. However, there’s one document that is essential to have ready, long before you even begin production.

bill of materials (BOM), or product recipe, is the DNA of a manufacturer’s product.

The purpose of having your multi level BOM is:

  1. Overview of Assemblies: To have greater details and specificity on the parent and sub-assemblies in the product, and their exact relationship between the sub assemblies and the finished product; and
  2. Prevent Errors when Dealing with Sub-Assemblies: If your manufacturing business is scaling, it becomes necessary to breakdown your products into sub-assemblies, and them into smaller sub-assemblies and components and so on, which will be essential in preventing errors and help accurately tracking parts.

As you can already see, it is important to know what is a sub assembly if you’re going to get more control over your multi level BOMs.

PRO TIP: If you’re a manufacturer and you have been struggling with inventory management, especially when it comes to handling raw material, we’d strongly recommend checking out resources for a manufacturing spreadsheet template.

This will help you get more control over your spreadsheets, and later when you decide to upgrade, the spreadsheet will be correctly formatted so you can easily import your inventory to your new management software.

Multi level BOM excel can be a tricky affair, especially if you’re handling variants and are tracking stock levels in spreadsheets too.

What is a Subassembly

This can be simply described as several components put together to make a unit, which can then be used as a part for a larger assembly, or a finished product.

A subassembly can also function as a finished product too, which can be sold separately to customers or used to finish the construction of another product.

It’s important to know what a subassembly is, as this is a key part of developing your multi level BOM.

This means you’ll need intimate knowledge of your materials, components, and subassemblies to carefully develop your indented bill of materials.

What Are Subassembly Examples?

As mentioned earlier in the article, subassembly examples will look like a BOM tree comprised of your raw materials, components, and subassemblies.

At the top of your tree will be your finished good (or parent product/level 0) and branching off from there will be all your subassemblies and their relation to the parent product.

Subassembly examples, for a bicycle, will look something like this:

As you can already see, intricate subassembly examples go into detail to show what exactly goes into the finished product, their inventory levels, and the workflow that needs to be followed to produce that product.

PRO TIP: The biggest issue for all manufacturing businesses, big and small, is finding a material requirements planning software. Especially for those who handle complex BOMs, that’s why it’s important to look into raw material inventory management to figure out how you can get more control over your inventory movements.

BOM structures resemble a family tree, with the parent item being the finished good and the children items being the subassemblies and their materials.

Is Excel the Best Option to Manage Multi Level BOMs

It is possible to save and keep a multi level BOM spreadsheet. A spreadsheet may seem like the obvious choice to manage your multi level bill of materials, but is it the best?

  1. Prone to Errors
    From copy/paste errors to more complex macro and script issues, BOMs kept in inefficient Excel spreadsheets can easily be plagued with issues and will need to be constantly updated manually, which will take up a lot of your resources. Not only does it waste time, but it can also mean that key business decisions are being made based on inaccurate data.
  2. Difficult to Add Variants
    It is difficult to add in your potential product variants. When a product has multiple variants, it can be complicated to manage in Excel as the number of resolved BOM’s will grow exponentially with the number of variants, very quickly becoming impossible to manage.
  3. Calculating Costs and Quantities
    Calculating totals in Excel may seem simple, and it is for flat or single level BOMs. However, when dealing with multi level BOMs it is more complicated. Calculating costs and quantities for multi level BOMs requires extensive set up, complex formulas and VLOOKUPs – to name just a few. This takes valuable time away from other important tasks and with increased complexity, it can result in errors.
  4. Creating a Multi Level (Indented) BOM is Complicated
    Creating a multi level BOM in Excel is not impossible but can be complicated. You need to be able to find a way to indicate a level of hierarchy across parts and sub assemblies. The reason that this is so difficult is that:

    • If you need add or remove any parts from your existing multi level BOM, you can easily make human errors. For example, are you inserting the new value in the right places, or if removing a sub assembly have you also accidently deleted all the associated parts as well? Small mistakes can lead to huge errors, if you are making business decision based on incorrect data.
    • The sorting function in Excel is incredibly useful but it can also cause major problems. For example, sorting columns can mess up your key columns and delay your production process.
    • When manufacturing various products, they will often use the same parts. Managing multiple instances of a part across products across differing levels of the BOM hierarchy can cause serious issues in Excel. For example, if you update the part number for a part for one product, will all instances of the part in the BOM be updated?

So, if Excel or any other type of spreadsheet documentation isn’t reliable, what options are there for manufacturing businesses looking to get more control over their multi level BOMs?

Smart Manufacturing Software for Multi level BOM Management

Adopting a smart manufacturing software, like the one offered by Katana, into your manufacturing business is going to mean more control over your multi level BOMs.

Katana, a bill of materials software developed by manufacturers, for manufacturers, centralizes your entire business (from your sales channels to manufacturing operations) to one, ridiculously easy to read, visual dashboard.

But, more importantly, Katana gives manufacturers the tools to get more control over their multi level BOMs, with accurate costings for seven layers deep into their BOM level.

So how does Katana achieve this? Let’s use the subassembly examples of a bicycle manufacturer.

How to Create Bill of Materials in Katana?

Within Katana, when creating your BOMs, you’ll need to simply input your subassemblies as a product, which will later be used in the BOM for your finished product.

Subassembly examples could range from bicycle wheels to wheelbarrow frames.

As you can see above, the frame, gears, and wheels appear as individual products but will be used as the ingredients for making the bicycle.

However, if you select the materials tab, you can see all the components which have been used to make those subassemblies.

A multi level BOM in Katana doesn’t appear indented, but as a line to follow to find a products relation to another.

So, to begin adding in your subassemblies, simply follow these steps:

1. Select the ‘+’ symbol at the top of the dashboard and at the drop-down menu, select ‘New product card’

A multi level BOM excel is extremely difficult to handle.

2. Here, you can input the subassemblies’ information, including the sale costs, ingredient costs, operation costs, quantities, the required materials/components, and the production process to make the subassembly.

Without the right software to help you, it can be easy to input an error at a BOM level when trying to manually update.

3. Once you have done this for each subassembly, you can now create the BOM for your finished product.

Open a ‘New product card’ again, and this time when you’re imputing your ‘Product recipe / BOM’ instead of adding new material or using saved materials, select your subassemblies (which will appear as a product) and begin designing your multi-level BOM.

Multi level BOMs are an essential document that needs to be ready before production can begin.
Indented bill of materials makes producing complex products easier to follow their manufacturing processes.

And that’s it, it’s that simple to add multi-level BOMs!

However, we should mention that Katana doesn’t take the traditional approach of an indented bill of materials structure.

Instead, what will happen is if a sales order is generated, Katana’s unique auto-booking system will automatically allocate available finished goods to the order, so you can fulfill it as soon as possible.

BOM structures are important to bet right, as one mistake can lead to a huge problem on the production line.

Although, if no bicycles are available, you’ll need to click on the sales order to find more information as to why it’s not available:

Multi level BOM excel are extremely prone to errors.

As you can see above, there are no finished bicycles in stock, and the subassemblies aren’t expected to be ready anytime soon.

You’ll simply need to generate a manufacturing order (MO) by selecting “Make…” and select if you wish to ‘Make in batch’ or ‘make to order’

If you then go over to the MO screen by selecting ‘MAKE’ at the top of the dashboard, you can select the MO to get more information on the production status.

Whichever BOM level needs updating, it’s important to do it soon as to avoid problems on the factory floor. This is why finding the right smart manufacturing software.
Indented bill of materials make it easier to navigate which components go into your product.

In the above example, we don’t have the ingredients (subassemblies) to begin production, and we’ll need to create a manufacturing order (or place an order from the supplier in the case of the frame) for each of the subassemblies.


Once you’ve created those MO’s, if you return to the make screen, you can check on the status of each of your assembly’s production status.


Whichever BOM level needs updating, it’s important to do it soon as to avoid problems on the factory floor. This is why finding the right smart manufacturing software.

However, you’ve probably noticed that Katana schedules production by the older MO first, which might appear confusing if your first MO is dependent on the status of another MO.

But, have no fear, Katana’s nifty drag-and-drop system allows you to easily reorganize your workflow, and better still, if some materials are used in two MO’s, Katana will automatically reallocate your material, so the prioritized order can be fulfilled first.

And a long story short, that’s how Katana helps manufacturing businesses get more control over their multi-level BOMs.

To find out more about how BOMs work in Katana, please take the opportunity to check out the video below:




PRO TIP: Katana is built with powerful integration features, so if you’ve been keeping your BOMs stored in an e-commerce platform, you can easily import your products and synchronize your stock levels.

It doesn’t matter if you’ve been doing Shopify inventory management or WooCommerce inventory management, Katana can integrate with both.

Subassembly examples that can help you understand them more are all the components used to make a bicycle.

Multi-level BOMs can be a tricky element of your business to handle.

And looking at the indented bill of materials example, it’s largely due to a manufacturer having to follow, not only the production of their finished goods but their subassemblies too.

You’re going to need to keep up stock levels and develop a smooth production flow for a multi-level BOM to make sure that your production floor doesn’t come to a complete halt due to being understocked or a bottleneck occurring when creating a subassembly.

Fortunately, Katana is the all-in-one solution to help you avoid bad multi-level BOM management.

But, also allows you to quickly and easily get an entire overview of your business for improved management and production scheduling.

And if you’ve been using QuickBooks Online to monitor your business, no worries! Katana can integrate with your QuickBooks account, allowing you to improve your QuickBooks inventory management.

Don’t believe us? See for yourself! Katana offers a 14-day free trial, so you can experience firsthand how it can help you become a more disciplined manufacturer.

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