Mastering SOLIDWORKS Bill of Materials Equations

Article by James Carlin on Feb 05, 2024

In SOLIDWORKS, the Bill of Materials (BOM) serves as a central hub, providing vital information about an assembly's components and their quantities. But have you ever felt limited by its standard features? In this article, we cover the fundamentals of setting up BOM equations and show how equations work in the context of a BOM table. 

By the end, you will be equipped with the knowledge to:

  • Automate repetitive tasks - Automatically calculate total lengths, weights, or costs based on component properties, eliminating the need for manual calculations.
  • Dynamically update a BOM - Equations allow a BOM to automatically reflect changes in the design, ensuring accuracy and saving valuable time.
  • Gain valuable insights - Extract deeper meaning from your BOM by using equations to calculate ratios, percentages, and other relevant data points.

In this example, we have three wires made of different materials, diameters, and lengths. We need to display, in a BOM table, the weight of each wire in both pounds and kilograms, plus the lengths of the respective wires in inches and meters. That works out to about 12 separate manual inputs – and that’s for just three wires! What’s more, the wires aren’t straight. So, how can this be managed in a reasonable amount of time?  

SOLIDWORKS Bill of Materials Equations Wire Example

Here is where BOM equations can help. But, before we start inputting the equations, we must first develop formulas to calculate our needed values.

Length of Wire Formula

Any uniform wire can be hypothetically viewed as a cylinder, even if the wire is not straight. One way to calculate its length is to use two values: Circumference and outer Surface Area (minus end-faces).

SOLIDWORKS Circumference and outer Surface Area

Unroll the cylinder to get a rectangle:

Cylinder Surface Area in SOLIDWORKS

The formula would look something like this:

Length = (Surface Area) – (2 * End Face Area) / (Circumference) 

Length = (Surface Area) – (2 * End Face Area) / (Circumference)                                                    

In SOLIDWORKS, we can obtain Surface Area using the Mass Properties tool and the Diameter using the Measure tool. This information can be easily entered into a custom properties table:

Custom Properties Table in SOLIDWORKS

Now, let’s create a BOM table and add equations!

Double-click in the blue-lettering tabs above a column to choose the column type. Select EQUATION to have it apply to an entire column.

SOLIDWORKS BOM Equation Column Type

Next, click the sigma key  to open the Equation editor (this is where the formula is entered).

SOLIDWORKS BOM Equation Editor

In order to control the decimal place position, be sure to select Precision before entering the formula. In this case, we are converting pound weight to kilograms and want it reported to the thousandth. 

The steps to enter the formula are straightforward. Select Precision, then Custom properties dropdown menu to choose a linked value (e.g., Weight), then apply the conversion factor. 

Now, to enter the wire length formula: Length = (Surface Area) – (2 * End Face Area) / (Circumference) 

SOLIDWORKS Bill of Materials Length Equations

Next, we will add the length conversion for the meters column: 

Length Conversion SOLIDWORKS BOM

Notice the ∑ symbol in the top corner of each column. This can be clicked to immediately access the Equations editor for that column. 

Lastly, in addition to applying equations to entire columns, we can also apply them to individual cells in the table to add Totals, Sums, Averages, and other functions.

To do this, highlight a cell and click the Sigma button at the top right.

Sigma Button on SOLIDWORKS BOM

Notice the functions to choose from.

Function Options in SOLIDWORKS BOM Tables

For example, we can total any column by clicking on the bottom cell of the column and selecting TOTAL from the Functions menu. For clarity, you can type text into the formula field to tag the value.


If we need to total a Row:

Sum ofTotal Row in SOLIDWORKS BOMs

We can even sum random cells not in the same Row or Column:

Sum of Cells in SOLIDWORKS BOM Using Equations

SOLIDWORKS' Bill of Materials (BOM) is handy, but sometimes its standard features fall short. That's where BOM equations come in. In a nutshell, embracing BOM equations in SOLIDWORKS turbocharges your BOM, streamlining workflows, ensuring accuracy, and giving you a clearer view of your designs. Time to unlock that potential!




Our SOLIDWORKS CAD Cheat Sheet, featuring over 90 tips and tricks, will help speed up your process.

I hope you found this tutorial helpful. Check out more SOLIDWORKS tips and tricks listed below. Additionally, join the GoEngineer Community to participate in the conversation, create forum posts, and answer questions from other SOLIDWORKS users. 

More SOLIDWORKS Tutorials 

SOLIDWORKS Table Templates

SOLIDWORKS Tutorial - Bill of Materials [Video]

Display SOLIDWORKS Sheet Metal Surface Area in Your Bill of Materials

The Bomb of all BOM SOLIDWORKS Webinars [Video]

Using and Exporting BOMs from Inside SOLIDWORKS PDM



About James Carlin

James Carlin is a SOLIDWORKS Technical Support Engineer at GoEngineer.

View all posts by James Carlin