Molar Mass Calculator

About This Tool

The Molar Mass Calculator instantly computes the molar mass (molecular weight) of any chemical compound from its formula. Simply type a formula like H2O, NaCl, C6H12O6, or even complex compounds with parentheses like Ca(OH)2 and Al2(SO4)3, and the calculator parses each element, looks up its atomic mass, and sums the contributions to give you the total molar mass in grams per mole (g/mol).

What Is Molar Mass?

Molar mass is one of the most fundamental concepts in chemistry. It represents the mass of exactly one mole of a substance, where one mole contains Avogadro's number (6.022 × 10²³) of particles. The molar mass of an element equals its atomic mass from the periodic table, expressed in g/mol. For compounds, you add up the atomic masses of every atom in the molecular formula. This seemingly simple calculation underlies virtually all quantitative chemistry, from preparing solutions in a teaching lab to scaling industrial chemical processes.

How the Calculator Works

The calculator uses a formula parser that recognizes standard chemical notation. It identifies element symbols (one uppercase letter optionally followed by a lowercase letter), reads subscript numbers, and handles parenthesized groups with outer subscripts. For each identified element, it multiplies the atom count by the standard atomic mass (based on IUPAC 2021 values) and sums everything to produce the total molar mass. It also calculates percent composition automatically, showing you what fraction of the compound's mass each element contributes.

Practical Applications

Molar mass calculations are essential in stoichiometry, the branch of chemistry dealing with the quantitative relationships between reactants and products. When you need to measure out a specific number of moles of a reagent, you multiply the desired moles by the molar mass to get the mass in grams to weigh on a balance. For solution preparation, knowing the molar mass lets you calculate how many grams of solute to dissolve to achieve a target molarity. In analytical chemistry, molar mass connects mass spectrometry data to molecular identity.

Percent Composition and Empirical Formulas

The element breakdown table shows percent composition, which is the mass percentage each element contributes to the total compound. This information works in reverse too: if you know the percent composition from an experiment, you can determine the empirical formula of an unknown compound. Divide each element's mass percent by its atomic mass, then divide by the smallest result to get the simplest whole-number ratio. This is a standard technique in analytical and organic chemistry for identifying unknown substances.

Common Compounds and Their Molar Masses

Some molar masses are worth memorizing: water (H2O) is 18.015 g/mol, carbon dioxide (CO2) is 44.009 g/mol, glucose (C6H12O6) is 180.156 g/mol, and sodium chloride (NaCl) is 58.443 g/mol. These values appear constantly in chemistry coursework and laboratory work. The quick-select buttons above let you load these and other common compounds instantly.

Tips for Entering Formulas

Always capitalize element symbols correctly: Co is cobalt, but CO is carbon monoxide. Use parentheses for polyatomic groups: Mg(OH)2 not MgOH2. Subscript numbers go immediately after the element or closing parenthesis. The calculator supports most common elements found in general, organic, and biochemistry courses. If you get an error, double-check your element symbols against the periodic table.