Molar Mass Calculator
Compute molar mass of a chemical formula (H2O, C6H12O6, NaCl) by summing atomic weights. 50 most-used elements.
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.
Related Tools
Mole Calculator
Compute moles n = m/M (mass / molar mass). Useful for chemistry homework.
Polydispersity Index (PDI)
Calculate a polymer's polydispersity index (PDI), PDI = M_w ÷ M_n, dividing the weight-average molar mass (M_w) by the number-average molar mass (M_n). The dimensionless result (always ≥ 1) measures the breadth of the molar mass distribution: PDI = 1 means a monodisperse polymer (all chains the same size, rare, typical of living polymers); larger values mean a wide range of sizes. Commercial polymers have PDI of 2 to 20, depending on the polymerization process. PDI affects processability, strength and flow properties. Enter M_w and M_n.
Degree of Polymerization
Calculate a polymer chain's degree of polymerization, DP = M_n ÷ M₀, dividing the number-average molar mass of the chain (M_n) by the molar mass of the monomer or repeat unit (M₀). The dimensionless result is the average number of monomer units in each chain. The higher the degree of polymerization, the longer the chains and the more pronounced the polymer properties: increased mechanical strength, melt viscosity, transition temperature and toughness. Below a critical value, the material lacks typical polymer properties. Enter the chain molar mass and the monomer molar mass.
Molar Mass from Gas Density
Enter density in g/L, temperature in K and pressure in atm: M = ρ·R·T/P with R = 0.08206. A gas at 1.96 g/L, 273 K and 1 atm gives 43.9 g/mol.
Intrinsic Viscosity (Mark-Houwink)
Calculate a polymer's intrinsic viscosity by the Mark-Houwink-Sakurada equation, [η] = K·Mᵃ, from the constants K and a (specific to the polymer-solvent-temperature system) and the viscosity-average molar mass M. The result, in dL/g, relates the viscosity of a dilute polymer solution to its molar mass — the basis of molar mass determination by viscometry, a simple and cheap technique. The exponent a (between 0.5 and 0.8) reflects the chain conformation in the solvent: 0.5 for a theta solvent (coiled chain) and up to 1.0 for an extended chain in good solvent. Enter the constants K, a and the molar mass.
Corrosion Rate (Mass Loss)
Calculate the corrosion rate by the mass-loss method, CR = 87.6 × W ÷ (D × A × t), from the mass loss W (mg), the material density D (g/cm³), the exposed area A (cm²) and the exposure time t (hours). The result, in mm/year, is the average speed at which the metal is consumed by corrosion — the key parameter to predict the service life of structures, piping and equipment and to set the corrosion allowance in design. Rates below 0.1 mm/year are usually acceptable. Enter the mass loss, density, area and time.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.