How is the relative formula mass calculated?

The relative formula mass is determined by adding the relative atomic masses of all the atoms in the chemical formula of a compound. Each element has a specific average atomic mass based on the abundance of its isotopes, usually found on the periodic table. When calculating the relative formula mass, you consider the number of each type of atom present in the formula and multiply it by its respective relative atomic mass, then sum these values.

For example, in water (H₂O), you would take the relative atomic mass of hydrogen (approximately 1) and multiply it by the number of hydrogen atoms (2), and then add the relative atomic mass of oxygen (approximately 16) to get the total relative formula mass of water (2 x 1 + 16 = 18).

The other approaches do not reflect the method of calculating relative formula mass. Simply adding the total mass of a molecule is vague and does not take specific atomic masses into consideration. Multiplying the mass of individual atoms lacks the context of the necessary atomic masses and their respective quantities. Calculating the volume of the compound is unrelated to the mass and does not factor into any mass calculations.