Molar Mass Calculator

Molar mass: summing atomic masses

The molar mass of a molecule is the sum of the atomic masses of its constituent atoms, expressed in g/mol (numerically equal to the atomic mass in unified atomic mass units, u). For water H₂O: 2·1.008 + 15.999 ≈ 18.02 g/mol. For glucose C₆H₁₂O₆: 6·12.011 + 12·1.008 + 6·15.999 ≈ 180.16 g/mol. The molar mass equals Avogadro's constant (≈ 6.022×10²³ entities/mol) times the mass of a single molecule — that is, the mass of one mole of the substance. For pure isotopes or isotopically enriched samples (e.g. C-14 carbon, deuterated water D₂O), use the specific isotope's mass instead of the standard atomic weight. Atomic weights used here come from IUPAC's most recent table and reflect the natural terrestrial abundance.

Applications

Stoichiometry: balancing chemical reactions and converting between mass and moles of reactants/products. Solution preparation: calculating the grams of solute needed for a given volume at a target molarity (g = M · V · MM). Pharmacy and biology: dosing of active ingredients and concentration of biological buffers. Analytical chemistry: identification of compounds by mass spectrometry, comparing measured m/z with theoretical molar mass.

FAQ

What is the difference between molar mass and molecular mass? Molecular mass is for a single molecule (in u); molar mass is for one mole of molecules (in g/mol). Numerically they are the same.

Why do values change slightly between sources? Atomic weights are averages weighted by the isotopic abundance found on Earth, and IUPAC updates the recommended values periodically.

Does the tool handle isotopes like D (deuterium) or C-14? No — it uses the standard atomic weights of natural elements. For specific isotopes, compute manually using the isotopic mass.