The formula mass of a molecule is the sum of the atomic weights of the atoms in its empirical formula.
The molecular mass of a molecule is its average mass as calculated by adding together the atomic weights of the atoms in the molecular formula.
The molecular formula indicates the type and number of atoms in a molecule.
The formula mass is used to indicate the mole ratio of elements present in a compound.
The molecular formula of glucose is C6H12O6
The empirical formula of glucose would be CH2O.