Weight is directly related to mass, but it also
depends on the local gravity.
Acceleration is directly related to mass, but it also
depends on the net force acting on the mass.
Volume is directly related to mass, but it also
depends on the density of the object or sample.
Inertia is directly related to mass, and is completely determined
by the mass. It doesn't depend on anything else, so this may be
the best choice.
