Molar Mass Calculator

Molar Mass Guide

What Is Molar Mass?

Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance, expressed in grams per mole (g/mol). It equals the sum of the atomic masses of all atoms in the formula: H₂O = 2(1.008) + 15.999 = 18.015 g/mol. Molar mass is numerically equal to the relative molecular mass (Mr) but has units of g/mol. It bridges the macroscopic world (grams you can weigh) and the molecular world (atoms and molecules you cannot see).

Calculating Molar Mass from a Formula

Find each element's atomic mass from the periodic table, multiply by the number of that atom in the formula, and sum. Example: H₂SO₄ — H: 2 × 1.008 = 2.016; S: 1 × 32.06 = 32.06; O: 4 × 15.999 = 63.996. Total = 2.016 + 32.06 + 63.996 = 98.072 g/mol. Brackets mean multiply: Ca(OH)₂ = Ca + 2(O + H) = 40.078 + 2(15.999 + 1.008) = 74.093 g/mol. Always use the relative atomic mass from your periodic table — values differ slightly between exam boards.

Moles, Mass, and the Molar Mass Triangle

The fundamental relationship: moles = mass (g) ÷ molar mass (g/mol). Rearrangements: mass = moles × molar mass. Molar mass = mass ÷ moles. Example: how many moles in 49g of H₂SO₄? Moles = 49 ÷ 98.08 = 0.5 mol. This triangle is the most-used calculation in quantitative chemistry — every stoichiometry problem involves it. At A-level, you also need n = cV (moles = concentration × volume) for solutions, linking mass-based and volume-based mole calculations.

Real-World Applications

Molar mass calculations appear in: pharmaceutical chemistry (precise drug dosing — active ingredient mass must be exact). Food science (calculating nutritional content per serving, sugar analysis). Industrial chemistry (scaling reactions from lab to industrial quantities — a reaction needs a precise molar ratio of reactants). Environmental monitoring (converting pollutant concentrations between ppm by mass and mol/L). Every quantitative chemistry experiment — titrations, yield calculations, empi