Hi Rudy, sorry there isn't anything set up in MoI to do a volume calculation yet.
I do expect to add one along with some other analysis tools for version 2.0 though.
For now, you can use Rhino to do this calculation. This will even work with the free Evaluation version of Rhino which you can get here: http://download.mcneel.com/eval - open up your .3dm model in Rhino and type in "Volume" and that should tell it to you.
Thank you Michael.
Actually Today sombody told me about this trick in rhino (I have version 3.0), and all is great.
Then, having the volume of my piece, I can know my weight...