text: For any substance, the number density can be expressed in terms of its amount concentration c (in mol/m) as
  where  is the Avogadro constant. This is still true if the spatial dimension unit, metre, in both n and c is consistently replaced by any other spatial dimension unit, e.g. if n is in cm and c is in mol/cm, or if n is in L and c is in mol/L, etc.