SOLIDWORKS PDM BOMs Explained: Computed, Named and More

A SOLIDWORKS PDM BOM is a bill of materials that the vault builds and displays for you, without opening SOLIDWORKS. In SOLIDWORKS PDM Professional you will meet four kinds: the computed BOM (built live from file references), the named BOM (a saved, editable snapshot with its own workflow), the SOLIDWORKS BOM (read from BOM tables saved in your drawings and assemblies) and the weldment cut list BOM (read from cut lists in weldment parts). Each one can be shown indented, top level only, parts only or as a flat view BOM, and each one is formatted by a BOM layout that an administrator configures. This guide explains how they differ and when to use which.

Where the PDM BOM lives: the Bill of Materials tab

Select an assembly or drawing in the vault view in Windows Explorer and open the Bill of Materials tab in the file view pane. From there you pick:

• The BOM type (computed, named, SOLIDWORKS or weldment, depending on what exists for that file).
• The BOM layout, which decides the columns you see.
• The configuration of the assembly you want to report on.
• The version to show: the latest versions of all references or the versions as built.
• The view type: indented, top level only, parts only, or flattened.

None of this requires SOLIDWORKS: the data comes from the reference structure and variables already in the database, which is why purchasing and production love the PDM BOM.

The four SOLIDWORKS PDM BOM types

Computed BOM

The computed BOM is generated on the fly from the file references PDM recorded when the assembly or drawing was checked in. It is always “live”: every time you look at it, PDM walks the reference tree and pulls the variable values (part number, description, material and so on) from the data cards of each referenced file.

Because it is computed, you cannot edit it. If a description is wrong, you fix it on the part’s data card (or in the SOLIDWORKS custom properties, mapped to a variable) and the computed BOM reflects the change.

The computed BOM only knows what PDM knows. Purchased items that exist only as manual rows in a drawing table, and quantities driven by BOM table overrides in SOLIDWORKS, are not part of the file reference structure, so they will not show up the way they do on your drawing.

Named BOM

A named BOM is a saved copy of a computed BOM. You create it from the Bill of Materials tab with the save option, give it a name, and PDM stores it as its own object in the vault, linked to the source file.

Named BOMs are what you reach for when you need control:

• They can be edited. You can add rows for non-modeled items (paint, glue, packaging) or correct quantities without touching the CAD files.
• They can be checked out and checked in like a file, with version history.
• They can move through workflow states, so a named BOM can be reviewed and released separately from the CAD files.
• They do not change when the underlying parts change. That is the point: a named BOM is a snapshot of what you sent to manufacturing.

The trade-off is maintenance. A named BOM goes stale the moment the assembly changes, so you need a rule for when to create a new one (for example, at every release).

SOLIDWORKS BOM

When a drawing or assembly contains a BOM table and that file is checked in, PDM can read the table and show it as a SOLIDWORKS BOM. This is the BOM exactly as the designer formatted it, including table level overrides, item numbers and any manually entered rows.

The SOLIDWORKS BOM is the closest match to the printed drawing. It is also only as accurate as the designer’s table, and it is only updated when the file is saved and checked in again.

Weldment cut list BOM

For weldment parts, PDM can read the cut list and present it as a BOM. Each cut list item becomes a row, with the cut list properties (length, angle, description, material) available as columns through variable mapping. This is how you give the saw operator a list of members and lengths without a drawing. If structural members matter to you, our post on structural member support in PDM2Excel shows how those columns end up in Excel.

Which PDM BOM type should you use?

BOM type	Source	Editable	Own workflow	Best for
Computed	File references, live	No	No	Day to day lookups, where-used, quick checks
Named	Saved snapshot of a computed BOM	Yes	Yes	Release packages, ERP handoff, non-modeled items
SOLIDWORKS	BOM table saved in the file	No (edit in SOLIDWORKS)	No	Matching the drawing exactly
Weldment cut list	Cut list in a weldment part	No	No	Cut lists for fabrication

BOM views: indented, top level, parts only and flat view BOM

The view type changes how the same data is arranged.

• Indented shows the full tree with subassemblies and their children, each row indented under its parent. This is what most engineers expect.
• Top level only shows the direct children of the selected assembly. Subassemblies appear as single rows.
• Parts only removes the subassembly rows and lists the parts, with quantities rolled up.
• Flattened (the flat view BOM) lists the components of the whole structure at a single level, with quantities totaled instead of repeated per parent.

The flat view BOM is the one purchasing usually wants: one row per part number, total quantity. We wrote a full walkthrough in understanding the flattened BOM view in SOLIDWORKS PDM 2024, including how quantities roll up through nested subassemblies.

Configuring BOM layouts in the Administration tool

What columns appear in a PDM BOM is controlled by BOM layouts, which you manage in the Administration tool under the Bill of Materials node of the vault. A vault can have several layouts, for example an engineering layout and a purchasing layout.

When you edit a layout you decide:

1. Which columns exist and in what order.
2. Which variable each column reads. A “Description” column maps to your Description variable, a “Material” column to your Material variable, and so on. If the variable is empty on a data card, the cell is empty in the BOM.
3. Which BOM type the layout is for (computed, SOLIDWORKS or weldment).
4. Which users and groups may use the layout, through permissions.

Two habits save a lot of support calls. First, keep your variable mappings clean: a BOM column cannot show a value that never made it from the SOLIDWORKS custom properties into the database, and configuration specific properties need to be mapped to the right configuration. Second, keep the number of layouts small and named for their audience.

If you are exporting to Excel, the layout also defines what the export contains. Our guide on how to configure the SOLIDWORKS PDM bill of materials for PDM2Excel walks through a layout designed for clean exports.

Show as built vs latest versions

Every SOLIDWORKS PDM BOM can be shown against two different version sets:

• Latest versions resolve every reference to the newest version in the vault. This answers “what would this assembly contain if I opened it today?”
• As built resolves every reference to the version that was referenced when the assembly version you selected was checked in. This answers “what did this assembly actually contain at that point in time?”

The difference matters after release. If a part was revised after the assembly was released, the latest view will show the new revision’s data while the as built view shows the old one. When you hand a BOM to manufacturing or audit a past build, use as built on the released version of the assembly. When you are checking whether an assembly needs updating, compare the two.

Exporting a PDM BOM (and why not CSV)

The Bill of Materials tab can save a BOM to a file, and the obvious choice is CSV. We recommend against it. CSV loses formatting and data types, mangles part numbers with leading zeros, has no notion of the indented structure beyond a text column, depends on regional settings for its delimiter, and cannot carry thumbnails. We covered the pitfalls in detail in don’t export BOMs to CSV files.

What people really want is a native Excel file with a predictable layout that ERP or purchasing can consume, generated the same way every time.

Automating PDM BOM export

Manual exports do not scale. When someone has to remember to export the BOM at release, it will eventually be forgotten or exported with the wrong layout. For machine to machine handoffs (an ERP import, for example), the PDMShell bom command exports a BOM per layout from a script, a scheduled task or a workflow transition:

bom -filePath "Assembly.sldasm" -directory "C:\Exports" -layout "Purchasing" -configNames "Default"

It writes CSV, which is fine when software consumes the file and you control the parsing. The options are covered in automating bill of materials extraction using the PDMShell bom command and the PDMShell documentation. When people need the BOM, PDM2Excel exports it from the vault to a formatted Excel workbook, thumbnails included, using your existing BOM layouts.

If you pull BOMs through the PDM API yourself, getting a top-level only BOM using the SOLIDWORKS PDM API is a question that has come up on CADOverflow.

Common PDM BOM problems

• Empty columns. The variable is not mapped from the SOLIDWORKS custom property, is mapped to the wrong configuration, or the file was not checked in after the property was added.
• Missing components. Items that only exist as table rows in SOLIDWORKS do not appear in the computed BOM. Use a SOLIDWORKS BOM or a named BOM for those.
• Quantities differ from the drawing. The drawing BOM table may use overrides or a different configuration. Compare the configuration selected in the BOM tab with the one on the drawing.

Community discussions

• SolidWorks PDM BOM, how to get the bom using SQL when ShowChildComponentsInBOM is set on CADOverflow
• IEdmBomCell::GetVar config parameter is always returning an empty string on CADOverflow
• Get BOM from PDM Document on the SOLIDWORKS Forum
• best method to extract BOM from ePDM? on the SOLIDWORKS Forum

FAQ

What is the difference between a computed BOM and a named BOM in SOLIDWORKS PDM?

A computed BOM is generated live from file references and cannot be edited. A named BOM is a saved snapshot of a computed BOM that can be edited, versioned and moved through its own workflow.

What is a flat view BOM?

The flat view (flattened) BOM lists the components of the whole assembly at one level with totaled quantities. It is the view purchasing usually wants.

Why does my PDM BOM not match my drawing BOM table?

The computed BOM reads file references and data card variables, while the drawing table may include overrides, manual rows or a different configuration. Use the SOLIDWORKS BOM type to see the table as saved.

Can I export a SOLIDWORKS PDM BOM automatically?

Yes. A command line tool such as the PDMShell bom command can export BOMs from scripts, scheduled tasks or workflow transitions, so the export happens at release without anyone clicking anything.

Need help with this?

If you want BOM layouts that your ERP team can actually use, or automated BOM exports at release, contact us. You can also try PDMShell with a free trial.