How To Change Units In SolidWorks: A Definitive Guide To Document And System Precision

Users can modify measurement systems in SolidWorks by utilizing the Unit System toggle in the bottom-right Status Bar for immediate changes or navigating to Document Properties for granular precision and decimal control. Maintaining consistency between IPS (Inch, Pound, Second) and MMGS (Millimeter, Gram, Second) is critical for ensuring that manufacturing tolerances and mass property calculations remain synchronized with global engineering standards like ISO and ANSI.

Engineering Pre-Configurations and Template Architecture

Before modifying units within a live SolidWorks environment, engineers must distinguish between Document Properties and System Options. Document Properties are saved at the file level, meaning a change to a specific part or assembly does not globally alter the software’s behavior for future files. Conversely, System Options govern the overarching software interface. To ensure a streamlined workflow, users should prepare by auditing their current drafting standards and identifying the target output for their CNC or additive manufacturing partners.

Essential Pre-Procedure Checklist

• Software Access: SolidWorks 2018 or newer (the UI locations remain consistent across these versions).
• Drafting Standards Knowledge: Determination of whether the project requires ANSI (American National Standards Institute) or ISO (International Organization for Standardization) formatting.
• Template Path Awareness: Knowledge of the local or network file path where .prtdot, .asmdot, and .drwdot files are stored to make permanent unit changes.
• Precision Requirements: Determination of required decimal places (e.g., three-place decimals for standard machining vs. four or five for high-precision aerospace components).
• Estimated Duration: 2 minutes for a single-file change; 15 minutes for a full organizational template overhaul.

Master Workflow for Modifying SolidWorks Units and Drafting Standards

Navigating the SolidWorks interface requires an understanding of both the "Quick-Access" methods and the "Deep-Menu" configurations. Whether you are correcting a mistakenly started project in inches or setting up a new metric workflow, the following steps provide the technical roadmap.

Step 1: The Status Bar Quick-Toggle Method

The fastest way to change units in an active document is via the Status Bar located at the bottom-right corner of the SolidWorks window. This method is ideal for quick visual checks or when a specific component needs a temporary unit shift.

1. Locate the unit indicator in the bottom-right corner of the screen. It typically displays a code such as IPS, MMGS, CGS, or MKS.
2. Click the unit indicator to reveal a pop-up menu of standard unit systems.
3. Select the desired system from the list. The model will instantly update its internal database to reflect these units.
4. Verify the change by clicking on a sketch dimension or checking the Mass Properties window.

Pro-Tip: Changing units via the Status Bar does not change the drafting standard (e.g., moving from IPS to MMGS does not automatically switch you from ANSI to ISO). You must adjust the drafting standard separately if your drawing aesthetics must change.

Step 2: Advanced Configuration via Document Properties

For precision control over decimal places, rounding increments, and dual-dimensioning, you must access the Document Properties menu. This is the only way to define custom units that do not fit the standard IPS/MMGS templates.

1. Click the Options (gear icon) in the top toolbar or go to Tools > Options.
2. Select the Document Properties tab at the top of the dialog box.
3. On the left-hand pane, click on Units.
4. Under the Unit System selection, choose the radio button for your primary system. If you require a mix (e.g., millimeters for length but pounds for mass), select Custom.
5. In the main table, adjust the Decimals column for Length, Dual Dimension Length, and Angle.
6. Click OK to apply the changes to the current file.

Step 3: Implementing Dual Dimensions for Global Manufacturing

In a global supply chain, parts are often designed in one unit system but manufactured in another. SolidWorks allows for the simultaneous display of both metric and imperial units on drawings.

1. Within the Document Properties tab, navigate to Dimensions.
2. Check the box labeled Dual dimensions display.
3. Choose the position of the dual dimension (e.g., "On top" or "To the right").
4. Navigate to the Units sub-menu again to ensure the "Dual Dimension Length" units are set to the secondary measurement system you wish to display.

Warning: Excessive use of dual dimensions can clutter a drawing. Ensure the secondary units are set to a lower precision than the primary units to maintain visual hierarchy and readability for the machinist.

Step 4: Establishing Permanent Defaults via Template Modification

Changing units in every new part is inefficient. To make a unit system permanent for all future designs, you must modify your part, assembly, and drawing templates.

1. Open your default template file or create a new part file.
2. Follow the instructions in Step 2 to set your preferred units and precision.
3. Go to File > Save As.
4. Change the "Save as type" dropdown to Part Templates (.prtdot).
5. Navigate to your SolidWorks template folder (usually located in C:\ProgramData\SolidWorks\SOLIDWORKS 20XX\templates).
6. Overwrite the existing Part.prtdot file or save it with a new name like Metric_Part.prtdot.
7. Repeat this process for Assembly (.asmdot) and Drawing (.drwdot) templates.

Step 5: Overriding Units During Value Entry

SolidWorks possesses a powerful "Unit Intelligence" feature that allows users to enter dimensions in any unit, regardless of the document's active setting.

1. Open a sketch and select the Smart Dimension tool.
2. Click on an entity to open the Modify dialog box.
3. Type the numerical value followed by the unit abbreviation (e.g., 25.4mm or 1in).
4. Press Enter. SolidWorks will automatically convert that value into the document's native unit system while maintaining the exact physical length.

Comparative Matrix of Standard Unit Systems and Tolerancing Thresholds

The following table outlines the technical specifications of the primary unit systems used within SolidWorks and their typical engineering applications.

Resolving Unit Discrepancies and Template Synchronization Errors

Unit errors often manifest during the translation of files between different departments or when importing vendor-supplied STEP files. Below are the most frequent failure scenarios and their technical resolutions.

• Scenario: Mass Properties are Reporting Incorrect Weights

  
  
  
  • Root Cause: The document units for mass (grams vs. pounds) are mismatched with the material density defined in the Material Database.
  • Actionable Fix: Go to Tools > Mass Properties > Options. Select "Use custom settings" and ensure the units match your required reporting standard. Verify the material density in the Material Editor is defined in the same unit family.

• Scenario: Units Revert to Inches Every Time a New File is Started

  
  
  
  • Root Cause: The default system template is set to IPS, and the user is only changing the document units, not the template file itself.
  • Actionable Fix: Open the blank template, change the units via Document Properties, and use the Save As command to overwrite the .prtdot or .asmdot file in the system's template directory.

• Scenario: Imported STEP/IGES Files Show Strange Dimensions

  
  
  
  • Root Cause: SolidWorks imports neutral CAD files using the units defined in the export source, which may not align with your workspace settings.
  • Actionable Fix: Check the Status Bar immediately after import. If the units are wrong, use the Quick-Toggle method. If the scale is physically incorrect (e.g., the part is 25.4x too large), use the Scale feature under Features > Modify > Scale to normalize the geometry to 1:1.

• Scenario: Dimension Precision is Rounded Too Aggressively

  
  
  
  • Root Cause: The "Primary Precision" setting in Document Properties is set to fewer decimal places than the design intent requires.
  • Actionable Fix: Navigate to Document Properties > Units. Increase the "Decimals" count for Length. Note that this affects display only; SolidWorks internally calculates to many more decimal places than are displayed.

Frequently Asked Questions

How do I change units in an existing SolidWorks assembly?

Changing units in an assembly follows the same process as a part file: use the Status Bar toggle or the Document Properties menu. However, note that changing the assembly's units does not automatically change the units of the individual parts contained within it; those must be changed at the part file level if you wish for their internal metadata to reflect the new system.

Can I display fractions instead of decimals for inch units?

Yes. In the Document Properties > Units menu, select IPS as your system. In the Length row, change the "Decimals" dropdown to Fractions. You can then specify the denominator (e.g., 1/16, 1/64) and whether you want to round to the nearest fraction or display the decimal equivalent.

Why are my dimensions appearing in both mm and inches?

This occurs because the Dual Dimensions setting is enabled in your Document Properties or within the specific dimension's Property Manager. To disable this, go to Document Properties > Dimensions and uncheck the "Dual dimensions display" box, or select the specific dimension and uncheck the dual dimension option in the side panel.

Does changing units affect the physical size of my model?

No, changing units in SolidWorks does not scale the model; it only changes the "label" and the numerical representation of the geometry. For example, a 1-inch line will automatically become a 25.4mm line when you switch systems. If the part needs to be physically larger or smaller, you must use the Scale tool.

How do I set different units for different properties, like length in mm and weight in kg?

To achieve this, you must use the Custom unit system setting. Go to Document Properties > Units, select the Custom radio button, and then manually select your preferred unit for each category (Length, Dual Dimension, Angle, Mass/Section Properties).

Optimize Your Engineering Workflow

Mastering unit management is the first step toward creating professional-grade, manufacturable CAD models that adhere to global standards. For more advanced tutorials on parametric modeling and mechanical simulation, explore our comprehensive technical library.