What is Molecular Mass?

In short

The molecular mass of a substance is the sum of the atomic masses of all the atoms in one molecule. It is measured in atomic mass units (u).

In simple words

The unit is the atomic mass unit, $1\ \text{u} = \dfrac{1}{12}$ of the mass of one carbon-12 atom, which is $1.66 \times 10^{-27}\ \text{kg}$ . The relative molecular mass has no unit, because it is a ratio. The mass of one mole of the substance in grams has the same number and is called the molar mass, in $\text{g/mol}$ . For ionic compounds, which have no molecules, we say formula mass.

Example

For carbon dioxide, $\text{CO}_2$ : $12\ \text{u} + 2 \times 16\ \text{u} = 44\ \text{u}$ . The molar mass is $44\ \text{g/mol}$ .

Also searched as: molecular mass unit, units of molecular mass, unit of molecular mass, unit mass formula.