How to calculate molar mass

Molar mass (in g/mol) is how much 1 mole of a substance weighs. Finding it means adding the atomic masses of the elements in the formula.

Step by step

1. Identify each element and how many atoms there are (the number after it).
2. Multiply each atomic mass by its count.
3. Add it all up.

Example: water (H₂O)

2 × 1.008 (H) + 1 × 15.999 (O) = 18.015 g/mol.

With parentheses

In Ca(OH)₂, the subscript 2 multiplies the (OH) group: 40.078 + 2 × (15.999 + 1.008) = 74.09 g/mol.

What it's for

Molar mass is the bridge between grams and moles: moles = mass (g) ÷ molar mass. It's essential in stoichiometry (calculating a reaction's reactants and products) and in preparing solutions of known concentration.

FAQ

Is molar mass the same as atomic mass? Atomic mass is for an element (in u); molar mass is for the whole substance, in g/mol, and numerically equal to the sum of the atomic masses.

What is 1 mole? 6.022 × 10²³ particles (Avogadro's number) — chemistry's "dozen", used because atoms are far too small to count individually.