Molecular Weight Calculator

Enter a formula and this tool returns its molecular weight along with the key properties chemists, biologists, and materials scientists rely on for stoichiometry, yield predictions, and pharmaceutical development. The figure underpins a surprising amount of laboratory work, and demand for that precision keeps growing: the global market for molecular weight standards is projected to top $500 million by 2026.

Calculation works by adding up the atomic weights of every atom in the formula you supply, drawing on the latest IUPAC-recommended standard atomic weights. Where an element has several isotopes, the result uses the weighted average atomic mass according to natural isotopic abundance. That method holds accuracy to roughly 0.001 amu for most common compounds.

Input formatting matters more than people expect. Capitalization has to be exact, so 'H2O' is read correctly while 'h2o' is not, and atom counts depend on proper subscript notation. The error that trips up users most often is dropping the parentheses around a polyatomic ion that repeats, which throws off the atom count. When a formula is unfamiliar, it pays to verify it against a trusted reference before relying on the output.