- https://docs.aspose.com/svg/net/drawing-basics/coordinate-sy...
- https://www.w3.org/TR/SVG2/coords.html
- https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Po...
You can use “cm” and “mm” in SVG.
It will then be up to the viewer program (web browser or which ever program you are using) to make it correct for the DPI of your display.