Relative molecular mass (Mᵣ) is a dimensionless quantity equal to the average mass of a molecule relative to one-twelfth the mass of a carbon-12 atom; it has the same numerical value as the substance's molar mass in grams per mole. It is obtained by adding the relative atomic masses of all the atoms in the molecule. Being a ratio, it has no units.

相对分子质量(Mᵣ)是无量纲量,等于一个分子的平均质量相对于碳-12 原子质量十二分之一的比值;其数值与该物质以克每摩尔为单位的摩尔质量相同。它由分子中所有原子的相对原子质量相加得到。由于是比值,它没有单位。