Calculate the molecular weight of any chemical formula — enter a formula like H₂O or C₆H₁₂O₆ and get the molar mass in g/mol with element breakdown.
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Type the chemical formula using standard element symbols (e.g. H2O, NaCl, C6H12O6) — numbers indicate subscripts.
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Molecular weight (or molar mass) is the mass of one mole of a substance in grams per mole (g/mol). It equals the sum of the atomic masses of all atoms in a molecule. For water (H₂O): (2 × 1.008) + (1 × 15.999) = 18.015 g/mol. This means 18.015 grams of water contains 6.022 × 10²³ molecules (Avogadro\ number).
In a chemical formula, element symbols (e.g. H, C, Na) are followed by subscript numbers indicating how many atoms are present. H₂O = 2 hydrogen + 1 oxygen. C₆H₁₂O₆ (glucose) = 6 carbon + 12 hydrogen + 6 oxygen. Brackets indicate groups: Ca(OH)₂ = Ca + 2×(O+H) = Ca + 2O + 2H. This calculator accepts subscripts as plain numbers: H2O, C6H12O6, Ca(OH)2.
Avogadro\ number (Nₐ) = 6.02214076 × 10²³ mol⁻¹. It is the number of constituent particles (atoms, molecules, ions) in one mole of any substance. One mole of water (18 g) contains 6.022 × 10²³ molecules. One mole of carbon-12 is defined as exactly 12 grams. Avogadro\ number bridges the atomic and macroscopic worlds of chemistry.
Moles = Mass (g) ÷ Molar Mass (g/mol). Mass = Moles × Molar Mass. For glucose (C₆H₁₂O₆, MW = 180.16 g/mol): 90 grams = 90/180.16 = 0.4996 mol ≈ 0.5 mol. Understanding this conversion is fundamental to stoichiometry — calculating how much of each reactant and product is involved in a chemical reaction.
They are the same thing. Molecular weight (MW), molecular formula weight and molar mass all refer to the sum of atomic masses in the formula unit. For ionic compounds (like NaCl), it is more technically correct to say "formula weight" since NaCl is not a discrete molecule but an ionic lattice, but the calculation method is identical.
Molar mass is essential for: stoichiometric calculations in reactions, preparing solutions of known molarity (M = n/V), determining empirical and molecular formulas from combustion analysis, mass spectrometry (instruments measure mass-to-charge ratios), pharmaceutical dosing (drug concentrations are often in mg/kg or mol/L) and polymer science (molecular weight distribution determines physical properties).
Isotopes are atoms of the same element with different numbers of neutrons, giving slightly different atomic masses. Carbon has two stable isotopes: C-12 (98.9%) and C-13 (1.1%). The standard atomic weight of carbon (12.011) is the natural abundance-weighted average. This is why atomic weights are not whole numbers. In mass spectrometry, individual isotopes can be resolved.
Natural proteins (polymers of amino acids) can reach molecular weights of several million Daltons (g/mol). Titin, the largest known protein, has a molecular weight of about 3,800,000 g/mol. Synthetic polymers and DNA molecules can reach even higher molecular weights. For comparison, water is 18 g/mol, glucose is 180 g/mol and haemoglobin is about 64,500 g/mol.
