How to change units from inches to millimeters in SolidWorks?
Short Answer
To change units from inches to millimeters in SolidWorks, use Document Properties and switch the document unit system to MMGS. Go to Tools > Options > Document Properties > Units, then set Length/Linear units to millimeters. This is the fastest common professional method. Limitation: this changes units and dimensions, not model size unless you scale geometry separately.
What You Need to Know Before
Warning: Changing units in SolidWorks can update displayed dimensions without resizing the actual part the way you expect if the model was originally drawn at the wrong scale. A common failure is assuming a 1-inch part will automatically become a 1-mm part instead of remaining the same physical size shown in millimeters.
How to Change Units from Inches to Millimeters in SolidWorks
Command: Options
Shortcut: No default keyboard shortcut
Quick Steps:
- Open the part, assembly, or drawing, then go to Tools > Options from the top menu.
- In the Options dialog, open the Document Properties tab, then click Units in the left panel.
- Set Unit system to MMGS (millimeter, gram, second) or change Length/Linear units to Millimeters, then click OK.
Variables & Settings
Key Setting: Unit system = MMGS
Expert Setting: The Unit system control changes the active document’s measurement standard. If needed, you can also manually set Length/Linear units to millimeters while checking related fields like precision so dimensions display correctly in drawings and model annotations.
Why it Fails
Cause 1 (Geometry): The model may have been created at the wrong size in inches, so changing to millimeters only changes unit interpretation and displayed values, not intended design scale.
Cause 2 (layers/Locks): In drawings, linked imported geometry or referenced model dimensions may not appear to update as expected if the sheet uses external references or locked dimension formatting.
Cause 3 (Command/Logic): Users often change System Options instead of Document Properties; System Options affects defaults for new files, not the currently open SolidWorks document.
Quick Fix & Best Practice
Quick Fix: Use Tools > Options > Document Properties > Units and set MMGS, then verify a known dimension with Smart Dimension to confirm the model is still at the correct physical size.
Manager’s Verdict: Use this method when the model was built correctly and only the document units need changing. Avoid relying on unit switching alone if the part was modeled at the wrong scale; in that case, correct the geometry or scale it intentionally.
FAQ
How do I make millimeters the default unit in SolidWorks?
Go to Tools > Options > System Options > Default Templates and use templates already set to MMGS.
Does changing from inches to millimeters rescale the model?
No, it usually changes the unit display and dimensions, not the actual physical geometry size.
Can I change units in a solidworks drawing only?
Yes, drawing document units can be changed in Document Properties > Units independently of other files.
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