How To Change Dimension Units In SolidWorks: A Complete Technical Guide

Changing dimension units in SolidWorks requires altering the active document properties via the Status Bar or Options menu for immediate model updates, or editing standard template files for permanent system-wide changes. SolidWorks natively stores model geometry using internal SI unit baselines (meters), allowing users to switch dynamically between Imperial (IPS) and Metric (MMGS, CGS, MKS) systems without altering underlying geometry or corrupting feature trees.

Prerequisites and Configuration Checklist for SolidWorks Unit Management

Before adjusting measurement systems across parts, assemblies, or drawing sheets, establish the scope of your changes. Unit adjustments in SolidWorks operate on two distinct levels: active document overrides and global template defaults. Understanding this distinction prevents downstream assembly mismatches, incorrect bill of materials (BOM) values, and scaling errors during STEP/IGES exports.

System Requirements and Operational Parameters

• Essential Software Components: Dassault Systèmes SolidWorks (Standard, Professional, or Premium, versions 2018 through 2024+), active write access to network or local Document Template folders (.prtdot, .asmdot, .drwdot).
• Mandatory Technical Standards: ASME Y14.5 (Dimensioning and Tolerancing) compliance for IPS drawings, ISO 128 / DIN standards for MMGS drawings, and organizational CAD drafting standards.
• Time and Effort Metrics: Active document unit change requires under 30 seconds; complete system-wide template reconfiguration requires 10 to 15 minutes.

Step-by-Step Workflows for Changing SolidWorks Dimension Units

Step 1: Execute Quick-Switch Unit Overrides via the Status Bar

The fastest method to alter unit systems in an open SolidWorks part, assembly, or drawing document is through the Unit System flyout menu embedded in the lower-right corner of the application interface.

1. Locate the Status Bar at the bottom right corner of the active SolidWorks graphical workspace.
2. Click the unit indicator tag (which displays abbreviations such as MMGS, IPS, CGS, or MKS).
3. Select your target measurement standard from the pop-up list:
   
   
   • IPS (inch, pound, second)
   • MMGS (millimeter, gram, second)
   • CGS (centimeter, gram, second)
   • MKS (meter, kilogram, second)
4. Select Edit Document Units from the top of the flyout menu if custom unit combinations (such as millimeters for length and pounds for mass) are required.

Pro-Tip: Utilizing the Status Bar method modifies only the currently active document. It does not alter your saved template configurations or affect newly created parts.

Step 2: Modify Unit System, Precision, and Rounding via Document Properties

When granular control over decimal precision, fraction display, mass properties, or angular units is required, navigate directly through the System Options menu.

1. Click the Options gear icon on the main menu bar, or select Tools > Options.
2. Navigate to the Document Properties tab at the top of the dialog box.
3. Select Units from the left-hand menu tree.
4. Under the Unit system panel, select a standard system or choose Custom to mix disparate units.
5. In the Basic Units table, define the specific parameters:
   
   
   • Set Length display units (e.g., Inches, Millimeters, Feet & Inches).
   • Adjust Decimals precision dropdowns (e.g., .00 for general tolerances, .0000 for precision machining).
   • Set Fractions and fraction denominators (e.g., 1/64) if working with Imperial architectures.
   • Define units for Angles, Mass/Section Properties, and Per Unit Volume.
6. Select your preferred rounding method under the Rounding section (e.g., Round half away from zero or Round half to even).
7. Click OK to save and apply the settings to the active file.

Warning: Decreasing decimal precision in Document Properties does not delete internal model accuracy, but it will round displayed dimensions on sketches and drawings, potentially hiding tight tolerance stacks.

Step 3: Permanently Update Default Part, Assembly, and Drawing Templates

If new documents continuously open in the wrong unit system (e.g., opening in IPS when your workspace requires MMGS), the underlying default document templates must be updated and re-saved.

1. Click File > New and open a blank document using your standard template (Part, Assembly, or Drawing).
2. Follow the steps in Step 2 to configure the desired Unit System, decimal precision, and drafting standard (ANSI/ISO).
3. Click File > Save As....
4. Change the Save as type dropdown to the corresponding template format:
   
   
   • Part Templates (*.prtdot)
   • Assembly Templates (*.asmdot)
   • Drawing Templates (*.drwdot)
5. Overwrite the existing default template file inside your designated template directory (typically located at C:\ProgramData\SOLIDWORKS\SOLIDWORKS 20XX\templates), or save it under a custom naming convention (e.g., MMGS_Part_Template.prtdot).
6. Navigate to Tools > Options > System Options > Default Templates and confirm that SolidWorks points to your newly saved template files.

Step 4: Configure Dual Dimensions on Engineering Drawing Sheets

For manufacturing environments that require both Metric and Imperial callouts simultaneously, dual dimensions can be activated across drawing views without altering the primary model geometry.

1. Open the target SolidWorks Drawing document (.slddrw).
2. Navigate to Tools > Options > Document Properties > Dimensions.
3. Check the Display dual dimensions checkbox.
4. Define the Dual dimension position (e.g., On the right, On the bottom, or Top/Bottom with split leader).
5. Expand the Dimensions tree item on the left, select Units, and scroll to the Secondary Units section.
6. Specify the secondary unit system (e.g., convert primary MMGS drawing callouts to show secondary IPS values in brackets).
7. Click OK to execute. Existing and future dimensions will now display dual values automatically.

Step 5: Execute Inline Unit Overrides During Sketching and Feature Creation

SolidWorks allows real-time unit mixing within dimension input fields. This eliminates the need to change global document settings when working with vendor components specified in alternate units.

1. Double-click any driving dimension or open a sketch tool (e.g., Smart Dimension).
2. Type the numeric value followed directly by the unit abbreviation inside the Modify dialog box:
   
   
   • Type 25.4mm inside an IPS document; SolidWorks converts it to 1.00in.
   • Type 0.5in or 1/2in inside an MMGS document; SolidWorks converts it to 12.70mm.
   • Type 2.5ft or 100m for large-scale structural members.
3. Use the Equation Editor to combine mathematical operations with mixed units (e.g., ="Length@Sketch1" + 5mm - 0.125in).
4. Press Enter or click the green checkmark. SolidWorks converts the input to the document's primary unit system while maintaining exact physical length.

Technical Comparison of Standard SolidWorks Unit Systems

The following matrix highlights the operational parameters, display metrics, and standard industry use cases for the native unit systems available inside SolidWorks.

SolidWorks Unit Conversion Failures and Troubleshooting Protocols

Issue 1: Imported STEP/IGES Geometry Displays Incorrect Scale (25.4x Factor Off)

• Root Cause: The neutral CAD file was exported without explicit unit headers, causing SolidWorks to import unitless floating point values using system default templates.
• Actionable Fix: Go to Tools > Options > System Options > Import. Under the General settings, set File units to Try to derive from file, or check Customize curve import. Alternatively, open the imported part, insert a Scale Feature (Insert > Features > Scale), set the scale origin to Centroid or Coordinate System, and apply a scaling factor of 25.4 (for inch-to-mm) or 0.0393701 (for mm-to-inch).

Issue 2: Drawing Dimensions Fail to Update After Changing Part File Units

• Root Cause: Drawing document properties are decoupled from model document properties to allow multi-model assembly drawings with distinct sheet standards.
• Actionable Fix: Open the drawing file independently. Click the Status Bar unit toggle in the lower right corner and switch it to match the model. To permanently sync drawings, open the drawing template (.drwdot), set units via Document Properties > Units, and re-save the template.

Issue 3: Mass Properties Yield Astronomical or Near-Zero Results

• Root Cause: Discrepancy between mass units and volume density settings within Document Properties (e.g., calculating a large structural weldment in MMGS where mass defaults to grams instead of kilograms).
• Actionable Fix: Open the Mass Properties tool under the Evaluate tab. Click Options..., check Use custom settings, and manually reassign the Mass unit to Kilograms or Pounds, and the Volume unit to Cubic Meters or Cubic Feet.

Issue 4: Sketch Dimensions Display Fractions Instead of Decimals

• Root Cause: Document Properties units are set to IPS with Fractions enabled under the basic length settings.
• Actionable Fix: Go to Tools > Options > Document Properties > Units. Under the Length row, locate the Fractions column and select Decimal from the dropdown menu. Set decimal places to .000 or higher.

Frequently Asked Questions

Why do my SolidWorks dimensions revert to inches every time I create a new part?

Your default part template (.prtdot) is configured to IPS. To change this permanently, create a new part, switch the unit system to MMGS via the status bar, click File > Save As, change the file type to Part Template (*.prtdot), and overwrite your default template file.

Does changing units in SolidWorks alter the physical size of the 3D model?

No. SolidWorks uses unit-invariant geometry matrices. A 1-inch cube will automatically re-evaluate to 25.4 millimeters when you switch unit systems. The physical geometry remains identical; only the numerical values on dimensions and callouts change.

How do I override units for a single dimension without changing the whole part?

Double-click the dimension to open the Modify box. Type the explicit unit suffix directly after the number (e.g., type 50mm in an inch document or 2in in a metric document). SolidWorks converts the entry to the native document unit while calculating the precise physical length.

How can I show both Millimeters and Inches on a SolidWorks drawing sheet?

Go to Tools > Options > Document Properties > Dimensions. Check the box for Display dual dimensions. Next, navigate to Document Properties > Units and define your secondary units (e.g., Inches) under the Secondary Units section.

What is the difference between System Options and Document Properties in SolidWorks?

System Options apply globally to the entire SolidWorks installation across all open files and affect user interface behavior. Document Properties apply exclusively to the currently open file (or template) and dictate geometry display, draft standards, units, and material performance parameters.

Optimize Your CAD Workflow and Template Standardization

Standardizing your organization's CAD environment prevents costly downstream manufacturing errors caused by mixed measurement systems. Establish verified part, assembly, and drawing templates across your design team to ensure seamless unit alignment from initial sketch to final production output.