Volume of cell mesh, how to calculate

I am trying to calculate the volume of the polygonal mesh which is my plaque visualization. When I run in contour, cell size filter, it gives me result like [2.30944e+07, 2.30944e+07]. What does it mean and why there is written double? How can I add unit µm to it? How to properly scale the render, I used properties ->transforming->scale 1.3 1.3 1, looks pretty decent to me, when compared to ZEN Blue render.
I have no idea how to run R scripts about which I was reading in all guidebooks about Paraview and forums as well.