How to Calculate Molar Mass

The molar mass of a substance is the mass of one mole of it, in grams per mole. Because a mole is a fixed number of particles, molar mass is simply the sum of the atomic masses of every atom in the formula — the bridge between the mass you can weigh and the number of moles a reaction actually uses.

You find each element's atomic mass on the periodic table. Hydrogen is about 1.008, carbon 12.011, oxygen 15.999, and so on. Adding these up for a formula gives its molar mass.

Break the formula into elements, count how many atoms of each there are, multiply by the atomic masses, and add. Water, H₂O, has two hydrogens and one oxygen: 2 × 1.008 + 15.999 = 18.015 g/mol.

For a bigger example, sulfuric acid H₂SO₄ is 2 × 1.008 (hydrogen) + 32.06 (sulfur) + 4 × 15.999 (oxygen) = 98.07 g/mol. The calculator does this instantly and shows each element's contribution.

When a formula uses parentheses, the subscript after them multiplies everything inside. Calcium hydroxide, Ca(OH)₂, has one calcium plus two oxygen and two hydrogen: 40.078 + 2 × (15.999 + 1.008) = 74.09 g/mol.

Hydrates are written with a dot and a number of water molecules, like copper sulfate pentahydrate, CuSO₄·5H₂O. Add the mass of the five waters (5 × 18.015) to the anhydrous salt to get about 249.68 g/mol. The calculator handles both patterns automatically.