Calculation of volume fraction of buckpaper

Hi,
I have been working on buckypaper, where I’ve used a bead spring model for carbon nanotubes. I want to calculate volume fraction of atoms in the simulation box.
I used Voronoi analysis in OVITO for atomic volume (volume of each atom). Still, it is the same as the volume of the simulation box despite empty spaces between the beads?

Please help

Thank You