AutoCAD is the most widely used computer-aided drafting software in the world. It is capable of both two- and three-dimensional drawings. It can also create photorealistic images, allowing presentational tools such as fly-throughs to be created. Setting AutoCAD to work in metric units (meters, centimetres and millimetres) can be achieved easily.
Open AutoCAD. When it has loaded you will be presented with a blank drawing screen. At the command line, type "new," then hit "Enter."
Pick the acadiso.dwt file in the dialogue box that appears. This is the metric template file. The default file for US units is acad.dwt.
Click "Open" and you will be returned to the drawing screen. The drawing area is now a metric size, set as an A3 sheet of paper, which is 420mm x 297mm. You can now draw objects using metric measurements.
If you do swap between measurement types, double check which one you are using before you go too far with the drawing. Otherwise you may have to scale the drawing to set it to the right measurements.