Molecular Weight Calculator

About this calculator

The molecular weight (or molar mass) of a compound is the sum of the atomic weights of every atom in its chemical formula, expressed in grams per mole (g/mol). For water, H₂O, it's 2×(1.008) + 15.999 ≈ 18.015 g/mol; for glucose, C₆H₁₂O₆, it's 6×12.011 + 12×1.008 + 6×15.999 ≈ 180.16 g/mol. This calculator parses a chemical formula — including nested parentheses and subscripts like Ca(OH)₂ or Al₂(SO₄)₃ — and sums the atomic weights from the periodic table to give the total.

Molecular weight is one of the most fundamental numbers in chemistry: it's what converts between mass and moles (moles = mass ÷ molar mass), which is essential for stoichiometry, preparing solutions of a known molarity, and balancing chemical reactions by mass. Chemistry students, lab technicians and pharmacists use it constantly — for example, to weigh out the correct amount of a reagent for a titration or to calculate dosages from a compound's formula.