Molecular Weight Calculator — Molar Mass & Molecular Mass CalculatorMW = Σ(atomic mass × subscript) · g/mol · Da · amu · All 118 Elements
Use this free Molecular Weight Calculator to instantly compute the molar mass (g/mol) and molecular weight of any chemical compound, molecule, or formula unit by entering its chemical formula. The calculator automatically parses the formula, looks up the standard atomic weights of each element from the IUPAC periodic table, and sums all contributions using the formula: MW = Σ (atomic mass × number of atoms) — supporting all 118 elements of the periodic table, including brackets, parentheses, and complex polyatomic formulas. Results are expressed in g/mol (grams per mole) · Da (Daltons) · amu (atomic mass units) — the three standard units of molecular mass.
This online molar mass calculator is trusted across every area of chemistry and life sciences: A-Level, AP Chemistry, IB Chemistry, JEE, and NEET molar mass problems, stoichiometry and limiting reagent calculations, solution preparation — calculating mass needed for a target molarity (M = mol/L), pharmaceutical drug synthesis and molecular formula verification, biochemistry — protein, peptide, and nucleic acid molecular weight calculation, mass spectrometry data interpretation, and polymer and materials science molecular weight distribution analysis. Common compound examples — H₂O (18.015 g/mol), NaCl (58.44 g/mol), C₆H₁₂O₆ glucose (180.16 g/mol), CaCO₃ (100.09 g/mol), H₂SO₄ (98.08 g/mol) — are all supported instantly. Trusted by chemistry students, laboratory chemists, pharmacists, biochemists, and research scientists worldwide for fast, accurate molar mass determination.
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Molecular Weight Calculator — Molar Mass From Chemical Formula in Seconds
Molecular weight (molar mass) is the mass in grams of one mole of a substance, calculated by summing the atomic masses of all atoms in the formula. Water (H₂O): 2(1.008) + 15.999 = 18.015 g/mol. Glucose (C₆H₁₂O₆): 6(12.011) + 12(1.008) + 6(15.999) = 180.156 g/mol. This calculation underlies every stoichiometric calculation in chemistry — you cannot determine moles from grams without the molar mass. The molecular weight calculator parses chemical formulas including parentheses, hydrates, and charge notation to produce exact molar mass values.
Percent composition by element follows directly from molecular weight. In glucose (MW = 180.156): carbon contributes 6 × 12.011 = 72.066 g/mol, which is 72.066/180.156 = 40.0% by mass. Hydrogen contributes 6.7%; oxygen contributes 53.3%. Percent composition is used to identify unknowns from elemental analysis, to determine empirical formulas from experimental data, and to calculate the mass of each element in a sample. The calculator computes percent composition for every element in the formula alongside the total molar mass.
Isotopic molecular weights differ from average atomic weight molecular weights because isotopically pure compounds (used in NMR, mass spectrometry, and isotope labeling studies) have different masses from natural abundance averages. ¹²C has exact mass 12.0000 Da; ¹³C has exact mass 13.0034 Da. A protein labeled with ¹³C at all carbon positions will have a measurably different mass than the natural abundance protein. The calculator uses IUPAC standard atomic weights for routine chemistry and can optionally use monoisotopic masses for mass spectrometry applications.