Posted by dellus on Oct 22, 2021; 8:53pm
URL: https://forum.librecad.org/Changing-units-midway-through-a-drawing-tp5721140p5721143.html

LibreCAD basically just thinks in units only, whether inches, mm, miles, parsec or whatever mainly just is a naming (has some effects on dimensioning style and other minor things). If you switch a drawing from inches to mm a line 10 inches long will then be 10 mm long. You will have to scale the drawing manually accordingly (x25.4). It doesn't happen automatically.
To switch back to inches it's x1/25.4. So it's not very practical to do this midway through a drawing.

Also see here: https://dokuwiki.librecad.org/doku.php/usage:howto#how_to_convert_from_mm_to_inches