Relative atomic mass is defined as the ratio of the average atomic mass number of the different isotopes of that element which is weighted by abundance to the unified atomic mass unit. It is the weighted mean of the atomic masses of all the atoms of a chemical element found in a particular sample, weighted by isotopic abundance.

Relative atomic mass (RAM) of an element is the number of times one atom of an element is heavier than 1/12 the mass of an atom of carbon [C¹²].