Set Up Millimeter Units in Blender for 3D Printing

Configuring Blender to work accurately in millimeters is essential for designing dimensionally accurate models for 3D printing. This guide provides a straightforward, step-by-step walkthrough to adjust Blender’s scene units, viewport clipping distances, and grid scales to ensure your designs match real-world measurements and import properly into slicing software.

Step 1: Change Scene Units to Millimeters

  1. Open Blender and navigate to the Scene Properties tab in the Properties editor on the right (icon showing a cone, sphere, and cylinder).
  2. Expand the Units section.
  3. Set Unit System to Metric.
  4. Change Unit Scale to 0.001.
  5. Set Length to Millimeters.

Setting the Unit Scale to 0.001 ensures that one Blender unit equals one millimeter, preventing scale conversion issues when exporting to slicers like Cura, PrusaSlicer, or Bambu Studio.

Step 2: Adjust Viewport Clipping

Because the unit scale is now significantly smaller, the default camera clipping will cause geometry to disappear or clip through the view when you zoom in close.

  1. Press N in the 3D Viewport to open the right-hand Sidebar.
  2. Click the View tab.
  3. Under the Clip Start field, set the value to 0.1 mm (or 1 mm).
  4. Under the Clip End field, set the value to 1000 mm (or higher, depending on the size of your 3D printer bed).

Step 3: Adjust the Viewport Grid Scale

Align the background grid lines so they correspond to physical millimeter measurements.

  1. In the top-right corner of the 3D Viewport, click the dropdown arrow next to the Viewport Overlays icon (two overlapping circles).
  2. Locate the Grid settings.
  3. Change the Scale to 0.001.

The visible grid will now reflect 1 mm increments when zoomed in and larger metric increments when zoomed out.

Step 4: Verify Object Dimensions

  1. Select your object in the viewport.
  2. In the Sidebar (N key), go to the Item tab.
  3. View the Dimensions field to confirm that measurements are shown in millimeters (e.g., 20 mm, 50 mm).
  4. If you scale an object in Object Mode, always apply the scale by pressing Ctrl + A and selecting Apply All Transforms or Scale. This ensures modifiers and slicers interpret the dimensions correctly.

Step 5: Exporting for 3D Printing

When exporting your design to an .STL or .OBJ file:

  1. Go to File > Export > Stl (.stl).
  2. In the export panel on the right, ensure the Scale is set to 1.0.
  3. Check Apply Modifiers and, optionally, Selection Only.
  4. Click Export STL.

Your exported file will now maintain true 1:1 millimeter scale when loaded into any standard 3D printing slicer.