How to calculate molecular volume from the wavefunction?
the volume seems to be already in the output:

$\text{Molar volume}=305.994~\mathrm{bohr^3/mol}\ (27.304~\mathrm{cm^3/mol})$

But of course, this is defined with the volume inside a density contour of $0.001~\mathrm{e/bohr^3}$.  That may be different from what you measure, because volume is not a quantity with well defined meaning, and what you find in an experiment depends on how you measure it.  

Mathematically any atom or molecule have a volume of infinity since the electron spreads to the entire space, but this is clearly not the physically meaning of volume as we usually know it.