How To Change SolidWorks Units: The Complete Professional Guide
Changing units in SolidWorks requires updating both active document properties and permanent system document templates to prevent dimensional mismatch errors during downstream manufacturing. Mastering this workflow ensures seamless transitions between metric and imperial standards across parts, assemblies, and detailed engineering drawings.
Initial Setup Requirements & Pre-Operation Planning
Proper unit management prevents catastrophic tolerancing errors, incorrect mass property calculations, and downstream CNC machining failures. Before modifying parameters across your CAD environment, understanding the scope of document-level changes versus global template configurations is essential for maintaining design data integrity.
- Essential Equipment & Software: SolidWorks 2021 or later, active part, assembly, or drawing file, administrative access for template modifications.
- Mandatory Prerequisite Knowledge: Familiarity with ISO and ASME drafting standards, working knowledge of dual-dimensioning principles, and understanding of parametric design trees.
- Estimated Duration & Budget: 2 to 5 minutes execution time, zero direct financial cost, high long-term efficiency ROI for manufacturing prep.
Step-by-Step Procedure for Modifying SolidWorks Units
Step 1: Locate and Access the Document Properties Menu
Open your active SolidWorks file, navigate to the top standard menu bar, and click on Tools. From the dropdown menu, select Options, then click on the Document Properties tab located at the top of the dialog box. Alternatively, you can click the gear icon in the top right corner of the user interface, select System Options, and switch to the Document Properties tab.
Pro-Tip: You can quickly access the Document Properties dialog box by double-clicking the status bar units display located in the bottom-right corner of the SolidWorks window.
Step 2: Select the Target Unit System
Within the Document Properties tab, locate and click on the Units category in the left-hand column tree. Review the available predefined unit systems displayed in the main window panel, which include MKS (meter, kilogram, second), CKS (centimeter, gram, second), MMGS (millimeter, gram, second), and IPS (inch, pound, second). Select the radio button corresponding to your desired global measurement standard.
Warning: Changing the unit system of an active file directly scales the geometry unless you verify that the conversion scaling options match your precise engineering intent.
Step 3: Customize Decimal Precision and Unit Parameters
After selecting your base unit system, locate the Custom section at the bottom of the Units dialog box to modify individual unit types. You can independently adjust units for length, angle, mass, time, and force to meet specific industry standards. Set the desired decimal place precision for each parameter to ensure that manufacturing tolerances align with your machining capabilities.
Step 4: Save Changes to Permanent Templates
To ensure that your newly defined unit settings apply to all future parts, assemblies, and drawings, save the configuration to your root templates. Navigate back to File, select Save As, and choose Part Templates (*.prt; *.sldprt) from the save type dropdown. Overwrite your default company template or save it as a new custom template file path in your system options.
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SolidWorks Unit Systems and Precision Standards
| Unit System | Length Unit | Mass Unit | Time Unit | Typical Industry Application |
|---|---|---|---|---|
| IPS | Inches (in) | Pounds (lbs) | Seconds (s) | Aerospace and automotive design in North America |
| MMGS | Millimeters (mm) | Grams (g) | Seconds (s) | Global precision manufacturing, consumer electronics, ISO standards |
| MKS | Meters (m) | Kilograms (kg) | Seconds (s) | Large-scale civil engineering, heavy industrial machinery |
| CKS | Centimeters (cm) | Grams (g) | Seconds (s) | Specialized scientific research and academic modeling |
Common SolidWorks Unit Failures and Field Fixes
- Issue: Dimensions change scale unexpectedly after switching from millimeters to inches.
- Root Cause: SolidWorks scaled the underlying numerical value rather than converting the physical unit representation, causing dimensional blowout.
- Actionable Fix: Undo the action immediately, ensure the convert units option is properly checked in the unit settings dialog, and reapply the unit change.
- Issue: Drawings display different unit formats than the parent 3D part file.
- Root Cause: The drawing template possesses independent document properties that override or do not synchronize with incoming model dimensions.
- Actionable Fix: Open the drawing document properties, navigate to the drafting standard or units tab, and uncheck the box that uses custom drawing units, linking it directly to the model.
- Issue: Mass properties display unrealistic weights after unit modification.
- Root Cause: Material density was not properly updated or converted when the mass unit system shifted from metric grams to imperial pounds.
- Actionable Fix: Re-assign the material from the material database to automatically pull the correct density values matching your new unit system.
Frequently Asked Questions
How do I change units for a single dimension without changing the whole part?
You can override individual dimensions by clicking on the specific dimension in your graphics window, navigating to the Dimension PropertyManager on the left, and modifying the units or tolerance settings exclusively for that callout. This method isolates the change without altering the global document property settings.
Can I display dual units (inches and millimeters) on a SolidWorks drawing?
Yes, you can enable dual dimensions by going to Document Properties, selecting Dimensions, and checking the option to display dual dimensions. This allows your manufacturing drawings to display primary metric dimensions alongside secondary imperial dimensions in brackets.
Why do my new part files keep opening in inches instead of millimeters?
This occurs because your default part template is configured to IPS units. To fix this permanently, open a blank part file, change the units to MMGS, and save the file as a part template in your designated template folder, then set it as the default in System Options.
Does changing the units affect existing simulation and FEA studies?
Yes, modifying units in an active model with established simulation studies can corrupt boundary conditions, force loads, and mesh parameters. Always establish your target unit system before defining loads, fixtures, and material properties in SolidWorks Simulation.
How do I update mass properties to reflect new unit selections?
SolidWorks automatically recalculates mass properties based on the active unit system and assigned material density as soon as you apply changes in the Document Properties menu. You can verify the updated mass, volume, and surface area by navigating to Evaluate and clicking Mass Properties.
Streamline Your CAD Workflows Today
Mastering unit management in SolidWorks eliminates costly manufacturing errors and accelerates your path from initial concept to final production-ready documentation. Implement these template strategies across your engineering team today to ensure absolute dimensional consistency on every project.
