What is the correct calculation of the formula mass?

The formula mass is calculated by summing the atomic masses of all the atoms in a chemical formula. Each element's Atomic Mass is multiplied by the number of times that element appears in the formula, and then these values are added together. For example, in water (H₂O), the formula mass is calculated as (2 × atomic mass of H) + (1 × atomic mass of O). The result gives you the total mass of one mole of that compound in grams.