How do you calculate the atomic mass of carbon?

Atomic mass:

• The atomic mass of any element actually represents an atomic weight average the sum of the atomic masses of its naturally-occurring isotopes, each multiplied by their respective abundance.
• Its unit is Unified atomic mass and is denoted as $\mathrm{u}$.

Calculating the atomic mass of Carbon:

• The atomic number of Carbon is $6$.
• There are two major isotopes of Carbon $\mathrm{C}-12\mathrm{and}\mathrm{C}-13$ found in nature, having an abundance $98.89\%\mathrm{and}1.10\%$ respectively.
• To find the average mass of Carbon,

$$\begin{gathered} \mathrm{Average}\mathrm{mass}=\frac{(98.89\times 12)+(1.10\times 13)}{100} \\ \mathrm{Average}\mathrm{mass}=\frac{1200.3}{100} \\ \mathrm{Average}\mathrm{mass}=12.003\mathrm{u} \end{gathered}$$

Therefore, the average atomic mass of Carbon is $12.003u$