How To Change Units In SolidWorks: A Complete Professional Guide
Modifying units in SolidWorks requires adjusting the Document Properties to ensure your model’s linear and angular dimensions, mass properties, and manufacturing tolerances align with specific engineering standards like ISO or ANSI. By navigating to the Document Properties tab, users can define precision, unit types, and decimal places to maintain design integrity across assemblies and engineering drawings.
Pre-Operation Setup and System Requirements
Before modifying unit configurations, it is essential to understand that SolidWorks operates under a hierarchical system where Document Properties override System Options. Ensuring your unit system is correctly defined early in the design cycle prevents scaling errors, incorrect mass calculations, and assembly interference issues during the late-stage manufacturing phase.
- Software Prerequisites: Access to any version of SolidWorks (Standard, Professional, or Premium). No additional modules are required for basic unit adjustment.
- Mandatory Knowledge: Familiarity with the difference between System Options (affecting global application behavior) and Document Properties (affecting specific part or assembly files).
- Engineering Standards: Awareness of your target industry standard—typically ANSI (Inch-based) or ISO/DIN (Millimeter-based).
- Time Benchmark: The actual adjustment process takes less than 30 seconds; however, verifying downstream assembly alignment may take 5 to 10 minutes depending on file complexity.
- Essential Files: The active part (.SLDPRT), assembly (.SLDASM), or drawing (.SLDDRW) file you intend to modify.
Procedural Workflow for Modifying Unit Systems
Changing units within a SolidWorks environment involves a systematic navigation of the Document Properties menu. This process ensures that all subsequent sketches, features, and measurements adhere to the desired unit convention.
Step 1: Navigating to Document Properties
Open the desired part, assembly, or drawing file in SolidWorks. Navigate to the top menu bar, click on the Tools drop-down menu, and select Options. Alternatively, use the shortcut key combination Ctrl+Shift+O. Within the Options dialog, ensure you have the Document Properties tab selected rather than the System Options tab. If you are in the System Options tab, you will not see the Unit settings.
Step 2: Selecting the Unit System
In the left-hand column of the Document Properties window, click on the Units category. You will be presented with a list of system presets, including MKS (meter, kilogram, second), CGS (centimeter, gram, second), MMGS (millimeter, gram, second), and IPS (inch, pound, second). Select the radio button that corresponds to your project requirements.
Pro-Tip: If you require a custom unit system, such as a hybrid of millimeters for dimensions and inches for standard hardware, select Custom from the radio button list. This enables manual adjustment of individual unit types without affecting the global standard.
Step 3: Configuring Precision and Decimal Placement
Once the base system is selected, focus on the Basic Units table located at the bottom of the dialog box. Adjust the Decimal places for each category, such as Length, Angle, Mass/Section Properties, and Force. Standard industrial practice suggests a minimum of three decimal places for millimeter systems and four decimal places for inch systems to maintain an appropriate tolerance buffer for CNC machining and 3D printing.
Step 4: Applying Changes and Verifying Output
Click OK to commit the changes to the active document. Verify the update by creating a new sketch or measuring an existing feature using the Measure tool (found under the Evaluate tab). If the measurement values reflect the new unit system, the modification is successful. If you are working in an assembly, ensure that all sub-components are updated to match the master assembly unit system to avoid mass calculation errors.
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Technical Specifications and Engineering Standards Matrix
The following table outlines the standard configurations used in global engineering workflows. Selecting the appropriate system based on your regional and industry-specific requirements is critical for manufacturing compatibility.
| System Identifier | Base Length Unit | Base Mass Unit | Common Industry Application |
|---|---|---|---|
| IPS | Inch | Pound | Aerospace, Automotive (US), Oil & Gas |
| MMGS | Millimeter | Gram | General Manufacturing, Global ISO |
| MKS | Meter | Kilogram | Structural Civil Engineering, HVAC |
| CGS | Centimeter | Gram | Academic Research, Laboratory Equipment |
Troubleshooting Common Configuration Failures
Engineers frequently encounter inconsistencies when importing files from external vendors or legacy databases. Addressing these failures requires a disciplined approach to file verification.
- Root Cause: Scaling Errors During File Import. When importing STEP or IGES files, SolidWorks may default to the system units instead of the original file units, causing the model to be exponentially larger or smaller than intended.
- Actionable Fix: Re-import the file using the Import Options dialog. Ensure the Units setting within the Import dialog matches the intended scale of the source file. If the file is already imported, use the Scale feature under the Insert menu to correct the geometry size.
- Root Cause: Conflicting Units in Assemblies. An assembly containing parts with different unit systems (e.g., one metric part and one imperial part) often leads to confusion in the Bill of Materials (BOM) and Mass Properties.
- Actionable Fix: Open each part file individually and standardize the Unit system via Document Properties. Save each file, then rebuild the assembly. Use the Mass Properties tool in the Evaluate tab to verify that the total assembly weight aligns with physical expectations.
- Root Cause: Drawing Dimension Inconsistency. Dimensions placed on a drawing may not display the desired unit system if the drawing template properties differ from the part file properties.
- Actionable Fix: Open the drawing template, navigate to Document Properties, and ensure the Unit settings are configured to your required standard. Save this as a new Drawing Template (.drwdot) to prevent future recurring configuration errors.
Frequently Asked Questions
Does changing the unit system change the physical size of my part?
No, changing the unit system in SolidWorks is a display-based change. The underlying geometric data remains identical; the software simply converts the numerical representation of your features to match the new units.
Can I set a default unit system for all new files?
Yes, you can define global defaults by creating a custom template. Set your preferred units in a blank part, assembly, or drawing, then save these files as templates (.prtdot, .asmdot, .drwdot) in your designated template folder.
Will changing units affect my existing dimensions in a drawing?
If your dimensions are driven by the model, they will update automatically to reflect the new units. If you have manually overridden dimension text, those specific values will not update and may require manual correction to match the updated unit standard.
How do I handle mixed units for specific dimensions?
If you need a specific dimension to display in a different unit than the global document, you can override it in the Dimension PropertyManager. Under the Primary Value section, you can toggle between the document unit or a user-defined unit for that individual dimension.
Standardize Your Design Workflow Today
Maintaining consistent unit configurations across your projects is the foundation of error-free engineering and precision manufacturing. Implement these unit settings within your custom templates now to streamline your production cycle and eliminate common measurement discrepancies.
