In chemistry the numbers of atoms, molecules, or formula units, amount of substance, in a sample is reported in the SI unit “mole” (abbreviated mol). By definition 1 mole of objects contains the same number of objects as there are atoms in exactly 12 g of carbon-12 (i.e., Avogadro's constant = 6.0221 x 10^23).

A chemical substance may consist of atoms of a single element (e.g., O2), or of different elements (e.g., CO2). The molar mass of an element is the mass per mole of its atoms. The molar mass of a compound is the mass per mole of its molecules. The molar mass of an ionic compound is mass per mole of its formula units. To calculate the molar mass of a substance we add up the individual molar masses of the constituent atoms.

To use this calculator enter a chemical formula and tap OK, or alternatively, select a sample molecule from the menu. For example, if you needed the molar mass of sulfuric acid you would enter H2SO4. Parentheses can also be used: the formula for pentane could be entered as CH3(CH2)3CH3 or CH3CH2CH2CH2CH3.