# How do you calculate the atomic mass of carbon?

##### 1 Answer

The atomic mass of any element actually represents an *atomic weight average*, the sum of the atomic masses of its **naturally-occuring** isotopes, each multiplied by their respective **abundance**.

**Carbon** has only two naturally-occuring isotopes, Carbon-12 and Carbon-13, so both of their atomic masses will contribute to the atomic mass of carbon.

Notice that the famous **Nitrogen-14** atoms with neutrons).

**0.989** (or a percent abundance of 98.9%) and an atomic weight of **12.000000 u** (**u** represents atomic mass units).

**0.011** (or a percent abundance of 1.1%) and an atomic weight of **13.003355 u**.

The atomic mass of carbon is then determined to be

This is the value for carbon's atomic mass listed in the periodic table.

More on atomic weight average here: