# How does formula mass differ from atomic mass?

$\text{Formula mass}$ is the sum of the $\text{atomic masses}$.........
Take $C {O}_{2}$, the atomic mass of carbon is $12.011 \cdot g \cdot m o {l}^{-} 1$, that of oxygen is $15.999 \cdot g \cdot m o {l}^{-} 1$. Sum the atomic masses, i.e. $\left(12.011 + 2 \times 15.999\right) \cdot g \cdot m o {l}^{-} 1$, and we get $44.0 \cdot g \cdot m o {l}^{-} 1$, which is the formula mass of $\text{carbon dioxide}$.