[header] How to find molecular formula [title] Know the relationship between molecular and empirical formulae. [step] The empirical formula provides a ratio of atoms within a molecule, for example, two oxygens for every carbon. The molecular formula tells you how many of each of those atoms is present in the molecule. 
For example, one carbon and two oxygens (carbon dioxide). The two formulae are related by a whole number ratio such that if the empirical formula is multiplied by the ratio, it will yield the molecular formula.