Molar Mass Calculator

Molar mass is the mass of one mole (6.022 x 10^23 particles, Avogadro's number) of a substance, expressed in grams per mole, and it is the conversion factor chemists use to move between a measurable quantity -- mass on a balance -- and the number of particles or reacting units in stoichiometry. This calculator looks up a standard atomic weight for a selected element or sums the atomic weights of a selected compound's formula (values drawn from the IUPAC Commission on Isotopic Abundances and Atomic Weights' 2021 standard atomic weights report, such as 1.008 g/mol for hydrogen and 12.011 g/mol for carbon), then converts your entered quantity between grams and moles using that molar mass, and reports the corresponding particle count. Whichever unit you choose for the quantity field -- grams or moles -- only changes how that single entered number is interpreted; it does not change the looked-up molar mass itself, which depends only on which element or compound is selected.

That makes the quantity value completely independent of the molar mass result: you can change quantity freely and watch grams, moles, and molecule count update, while the molar mass display stays fixed until you pick a different substance. This is the same relationship used for solution preparation (weighing out a target number of moles of a reagent), stoichiometry problems (converting grams of a reactant to moles to use with a balanced equation), and general lab calculations.