Density and volume of simulation box

I am a little bit confused about the relation between density and volume of simulation box. How I determine the desired volume of simulation box at certain density? If I have density 0.98g/cm3 and the unit command is real, should I convert it to gm/ang3? and what is the volume of (region box block -30.0 30.0 -30.0 30.0 -30.0 30.0 units box)? is it 60^3 or 30^3?

Many thanks for your help

All the information you need is in the documentation page for the units command.
It states which units LAMMPS uses for different properties on input for length, mass, etc.
and also for output like density or pressure.

The remainder is a trivial exercise in calculus and common sense.