By default, Blender works in Metres (US: Meters). However, technical draftsmen and illustrators often prefer to work in millimeters even if the objects they are creating are many meters in size. To change to working in millimetres in Blender, we need to change a few default values in different places. It’s very easy to forget one of the steps involved:
Step 1 – Units and their Scale
Click the Scene Properties Tab 
expand the drop-down arrow next to Units and change/confirm the default values as follows:
- Unit System: Metric
- Unit Scale: 0.001
- Length: Millimeters
Step 2 – Grid scale
Next, we will need to change the scale of the ground plane grid. Click the Overlays Drop-down button:
Change the Floor Scale value to 0.001
Step 3 – Adjust the Clipping Values
Next, we type 
to bring up the menu tabs on the right hand side of the viewport. Blender people call this the “N” menu.
Click the View Tab: 
Change the clipping values to
- Clip Start: 1mm
- Clip End: 100 000
Click here to read a simple clipping explanation
Step 4 – Startup file
It would be painful if you had to perform all these steps every time you started a new blender drawing. So don’t forget to make this file into your startup file or modify these settings in your startup file itself.
For more about the Startup file, click here.
