How to Calculate Molar Mass

Add up the atoms

Molar mass is the mass of one mole of a substance in grams per mole. It is the sum of the atomic masses of every atom in the formula.

1. Count the atoms of each element. In H₂SO₄ there are 2 H, 1 S and 4 O.
2. Multiply each count by the element's atomic mass from the periodic table: H 1.008, S 32.06, O 15.999.
3. Add them: 2 × 1.008 + 32.06 + 4 × 15.999 = 98.07 g/mol.

Brackets and hydrates

A number after a bracket multiplies everything inside it: Ca(OH)₂ has 1 Ca, 2 O and 2 H. A dot joins water of crystallisation, so CuSO₄·5H₂O is copper sulfate plus five whole water molecules, 249.68 g/mol. Weigh out the hydrate using the hydrate's molar mass, not the anhydrous one.

Grams and moles

• Moles = mass ÷ molar mass. 49 g of sulfuric acid is 49 ÷ 98.07 = 0.50 mol.
• Mass = moles × molar mass.

Let the calculator count

Type any formula into the Molar Mass Calculator to get the molar mass and the mass percent of each element. To make a solution from it, use the Molarity Calculator.