An empirical (minimal) formula expresses the ratio of atoms in a substance using the smallest whole numbers. It can be determined directly from the percentage composition of a compound, but it does not by itself reveal the actual number of atoms in a molecule. For example, the empirical formula of hydrogen peroxide is HO, whereas its molecular formula is H₂O₂.

最简式(实验式)用最小整数比表示物质中各原子的比例。它可直接由化合物的百分组成测定,但本身并不能给出分子中原子的实际数目。例如,过氧化氢的最简式为 HO,而其分子式为 H₂O₂。