In Blender, there are default Unit System in Metrics. As per different scale of projects, like architecture and product visualization, you might need change to different unit system for your project. Below screenshot is a tip to quick change the units of rotation, Length, Mass, Time, and Temperature. For example, if you want to change the Length Unit from Meters to Centimetres (cm) or Millimetres (mm), we can go to the panel on the right-hand side, Scene Properties -> Units, make sure that the Unit System is “Metric”, expand the scroll-down menu of Length, then change the units to cm or mm. if you want to change the units to inches, you can switch the unit system to “Imperial”, then change the Length to Inches. Hope this helps! More Free Blender Tutorial here.
How to change units in Blender