How To Change Units On SolidWorks: A Complete Guide For Engineers
Changing units in SolidWorks involves toggling the measurement system dynamically via the status bar or redefining default document properties for length, mass, and time. Mastering both document-level adjustments and permanent template updates ensures compliance with international manufacturing tolerances and prevents costly fabrication errors.
Pre-Operation & Equipment Checklist
Establishing a streamlined parametric modeling workflow requires a firm grasp of how SolidWorks manages unit architecture. Unlike software that relies on a single global setting, SolidWorks divides its unit management between active document overrides and system-wide default templates. Neglecting to update these underlying parameters before detailing assemblies or generating machining drawings can result in severe dimensional discrepancies during CNC programming and rapid prototyping.
- Essential gear/tools/materials: SolidWorks desktop application (2018 through current releases), active part, assembly, or drawing file, and a baseline understanding of standard manufacturing metric and imperial tolerances.
- Mandatory prerequisite knowledge/standards: Familiarity with SI units (millimeters, grams, seconds) versus English units (inches, pounds, seconds), ANSI/ISO drawing drafting standards, and parametric tree structures.
- Estimated budget/duration benchmarks: Zero-cost operation requiring less than three minutes of configuration time per template.
Step-by-Step Procedure to Modify Measurement Systems
Step 1: Access the Status Bar Unit Toggle
Locate the status bar in the bottom right corner of the SolidWorks graphics window, which displays the currently active unit system such as MMGS (Millimeter, Gram, Second) or IPS (Inch, Pound, Second). Click directly on this unit readout to open a quick-selection flyout menu displaying the four primary default systems: IPS, MKS (Meter, Kilogram, Second), CGS (Centimeter, Gram, Second), and MMGS. Select your desired standard from this list to instantly update the active document environment.
Pro-Tip: The status bar toggle acts as an immediate override for the current active file only, making it the fastest method for addressing single-part drawing anomalies without altering system presets.
Step 2: Configure Custom Unit Parameters and Decimal Precision
Navigate to the top menu bar, select Tools, and choose Options to open the System Options and Document Properties dialog box. Click on the Document Properties tab at the top of the window, then select the Units category from the left-hand navigation tree. Within this panel, you can choose a predefined unit system or select Custom to manually define units for length, angle, mass, time, and stress. Adjust the decimal places and fractional display settings in the adjacent dropdown menus to match your required manufacturing tolerances, ranging from whole numbers up to eight decimal places.
Warning: Setting decimal precision too low in the unit properties menu can mask micro-level geometric overlaps, leading to interference errors in complex multi-part assemblies.
Step 3: Define Custom Mass and Force Properties
Within the Document Properties and Units dialog, locate the advanced specifications section governing mass, volume, and density metrics. If your project demands specialized aerospace or automotive calculations, verify that your force measurements are designated correctly in Newtons (N), pounds-force (lbf), or kilograms-force (kgf). Ensure that the volume display matches your downstream simulation requirements, switching seamlessly between cubic millimeters, cubic inches, or liters depending on fluid flow or thermal analysis parameters.
Step 4: Save Custom Settings as a Default Template
To ensure you never have to repeat these unit adjustments for future designs, save your configured document as a template. Go to File, select Save As, and choose SolidWorks Templates (*.prt.tpl, *.asm.tpl, *.drw.tpl) from the save-as-type dropdown. Navigate to your designated company template folder, name the file descriptively, and click Save. Update your System Options under File Location to point directly to this custom directory for seamless part initialization.
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SolidWorks Unit Systems and Physical Properties Comparison
| Unit System Name | Primary Length Unit | Primary Mass Unit | Time Unit | Common Engineering Application |
|---|---|---|---|---|
| MMGS | Millimeter (mm) | Gram (g) | Second (s) | Precision machine design, injection molding, consumer electronics |
| IPS | Inch (in) | Pound (lb) | Second (s) | Aerospace engineering, heavy structural fabrication, US manufacturing |
| CGS | Centimeter (cm) | Gram (g) | Second (s) | Scientific research, biomedical implants, optical engineering |
| MKS | Meter (m) | Kilogram (kg) | Second (s) | Large-scale civil engineering, architecture, heavy industrial plant layout |
Troubleshooting Unit Conversion Discrepancies
- Root Cause: Unintentional scaling issues after switching units, where a dimension originally modeled as 100 millimeters suddenly reads as 3.937 inches instead of being automatically scaled to 2.54 inches.
- Actionable Fix: Use the Scale tool under Insert, Features, Scale to explicitly resize geometry when transitioning between incompatible coordinate systems if the initial unit switch altered physical part dimensions.
- Root Cause: Drawing dimensions appearing in millimeters while the underlying part file was updated to inches.
- Actionable Fix: Open the drawing document properties, verify that the drawing units do not override part units, and ensure the option "Use document units" is checked under Document Properties, Dimensions.
- Root Cause: Mass properties displaying incorrect weights due to outdated material density calculations following a metric-to-imperial switch.
- Actionable Fix: Re-apply the material from the SolidWorks Material database to force the software to recalculate density using the newly active unit system.
Frequently Asked Questions
How do I change units in a SolidWorks drawing without affecting the part file?
Open the drawing sheet, go to Tools, Options, Document Properties, and select Units. Change the unit system or precision settings specifically within this drawing document. Because drawing properties can override part properties, modifying this menu alters the displayed dimensions on the sheet without changing the physical geometry of the 3D model.
Why do my dimensions change value when I switch from inches to millimeters?
SolidWorks defaults to a direct numeric translation when you switch systems via the status bar unless scaling is explicitly applied. If a part is drawn with a length of 10 units, switching from IPS to MMGS changes the length to 10 millimeters rather than converting 10 inches to 254 millimeters. Always use the Custom unit options or scale features to ensure physical size accuracy during major system transitions.
Can I set a default unit system for all new parts I create?
Yes, you can establish permanent default units by configuring a part, assembly, or drawing file with your preferred unit settings and saving it as a template file. Access Tools, Options, System Options, File Locations, and add your custom template directory to ensure SolidWorks utilizes your preferred measurement standard upon every new file startup.
How do I change mass properties units from pounds to grams?
Navigate to Tools, Options, Document Properties, and select Units. In the Unit system section, choose Custom, then locate the Mass/Density subsection within the lower half of the dialog window. Change the mass dropdown menu from pounds to grams, and adjust the decimal place settings to reflect your required level of mass precision.
Master your SolidWorks workflows today by standardizing your unit templates to eliminate costly manufacturing errors and accelerate your path to production.
