# How do you find relative atomic mass?

##### 1 Answer

Oct 4, 2016

#### Answer:

Find out the mean of all an atom's isotopic masses.

#### Explanation:

An atom's isotopic mass is the sum of its protons and neutrons - we'll exclude electrons because they've negligible weight. Then we work out the mean of its isotopes using their abundances.

For example, chlorine has two isotopes: