Relative atomic mass (Aᵣ) is a dimensionless quantity equal to the average mass of an atom of an element relative to one-twelfth the mass of a carbon-12 atom; it has the same numerical value as the element's molar mass in grams per mole. Being a ratio, it has no units. For example, the relative atomic mass of carbon is about 12.

相对原子质量(Aᵣ)是无量纲量,等于元素一个原子的平均质量相对于碳-12 原子质量十二分之一的比值;其数值与该元素以克每摩尔为单位的摩尔质量相同。由于是比值,它没有单位。例如,碳的相对原子质量约为 12。