An empirical formula is the simplest ratio of atoms of each element in a compound. You will be given either the mass of each element in the compound or the % mass. 1. Divide each mass (or % mass) by the atomic mass of the element (found in the periodic table). 2. Look at the numbers produced and identify the smallest number. 3. Divide each result from step 1 by the smallest number. 4. The resulting numbers is the ratio of each element. 5. Sometimes the numbers will need to be multiplied to produce whole numbers. 6. These whole numbers will be an empirical formula.