All of my solids were originally generated in FreeCad 0.19. In FreeCad 0.19 there is a handy macro called FCInfo. This will allow you to calculate what it calls in its GUI "Moment of inertia with mass". You can specify a density of a STEP solid. Great tutorial here called "FreeCAD Mass Properties - Weight, Volume, Area and More |JOKO ENGINEERING|" .
https://www.youtube.com/watch?v=gThQk...
What you can also do is use Blender or any other meshing program to scale your solids (in case things like moment of inertia disappear given a smaller sub-0.1m sized shapes). You can easily export your shape as a DAE or STL mesh, scale in Blender, then essentially convert back into a STEP-like shape in FreeCad, which will again allow you use the FCInfo to get physical parameters about the shape as well as change the density. Great tutorial about how to do that here called "FreeCAD 0.19 - Converting STL files to Solid models".
https://www.youtube.com/watch?v=GYc3B...
I was able to verify for a given shape I had used in MeshLab (tutorial in question), that given a density of 1kg/dm^3, the calculated moment of inertia with mass matched between MeshLab and FCInfo in FreeCad. Amazing the capability of open source software tools...
