A molecular formula is a formula that gives the actual number of atoms of each element present in one molecule of a substance. It conveys more information than the empirical formula, which gives only the simplest whole-number ratio of atoms. For example, the molecular formula of hydrogen peroxide is H₂O₂, whereas its empirical formula is HO.

分子式是表示一个分子中各元素原子实际数目的式子。它比只给出原子最简整数比的最简式包含更多信息。例如,过氧化氢的分子式为 H₂O₂,而其最简式为 HO。