Hi Marco, yes like Brian writes above there is not currently any way to get this data directly from MoI. I do plan on adding that in but for now you need to export your object to a different CAD program to get that information.

You can also export to STL format and there are various STL display/inspection programs that you can use which usually have volume calculations with them, here's one:
http://software.materialise.com/minimagics

- Michael