Getting Started with Blender for 3D Printing & CNC Modeling: How to Set Blender to Use Millimeters by Default

Whether you're preparing models for 3D printing, CNC machining, or any kind of precision manufacturing, Blender can be a powerful modeling tool when configured correctly. Out of the box, Blender uses meters as its default unit of measurement, which can be problematic for accurate, small-scale work. In this guide, we’ll walk you through how to set up Blender 4.5.0 to use millimeters as the default unit, ensuring your projects are correctly scaled for export into slicers or CAM software.

This is the first entry in our Blender for Makers series — a collection of tutorials designed specifically for those using Blender to create functional models for 3D printing, CNC routing, laser cutting, and beyond.

Why Use Millimeters in Blender?

Most slicers (like Cura, PrusaSlicer, and Bambu Studio) and CNC CAM tools (like Fusion 360, VCarve, and Carbide Create) expect STL or OBJ files to be modeled in millimeters. If your Blender model is built using meters or inconsistent scaling, it can lead to misaligned prints, incorrect tool paths, or scaling issues during export.

How to Set Blender to Use Millimeters by Default (Blender 4.5.0)

Follow these steps to configure Blender for precision modeling in millimeters:

🔧 Step-by-Step Instructions:

1. Launch Blender 4.5.0
   When the splash screen appears, simply click anywhere off to the side to close it.
   
   

2. Optional: Start with an Empty Scene
   If you prefer a clean workspace every time Blender opens, press A to select everything (the camera, light, and cube), then press X to delete them.
   
   

3. Open the Scene Properties Tab
   Look for the tab with the cone and sphere icon on the right-hand sidebar.
   
   

4. Configure Units for Precision Modeling
   
   

   • Expand the Units section.
     
     

   • Change the Unit System to Metric.
     
     

   • Set the Unit Scale to 0.001.
     
     

   • Finally, change Length to Millimeters.
     These changes ensure your modeling grid and object dimensions are properly scaled to millimeters — essential for 3D printing and CNC accuracy.
     
     

5. Adjust Grid Overlay to Match Unit Scale
   In the 3D Viewport Header, click the Overlay dropdown (the small down arrow in the top-right corner).
   Set the Scale to 0.001 so the visible grid reflects your new unit system.
   
   

6. Save as Your Default Startup File
   Once you're happy with your setup, go to File > Defaults > Save Startup File, and click OK to confirm.
   This ensures every new project will open with millimeters as the default unit, so you’re always ready to model for 3D printing or CNC fabrication.
   
   

✅ You're Ready to Model for 3D Printing and CNC

Now that Blender is configured to use millimeters, your modeling environment is optimized for real-world applications. Whether you’re designing 3D printed enclosures, CNC-cut panels, or laser-cut templates, this foundational setup will save time and prevent scaling headaches down the line.

Stay tuned as we continue the Blender for Makers series, where we’ll cover:

• Exporting clean STL/OBJ files
  
  

• Setting up modifiers for printability
  
  

• Modeling techniques for subtractive manufacturing
  
  

• And much more!