How LAMMPS calculate the denisty of simulation box

Dear sir,

My simulation box contains polymer & water molecules. I want to know how LAMMPS calculate the density of the simulation box.
Example - Polymer chain Molecular mass = 45720
Water molecules(100) molecular mass = 1800
Box size = 50 * 50 * 50 Angstrom

Is there more than one possibility (density = total mass/volume) ?

Understood sir

Thanks, sir