Molar Mass Calculator

How it is calculated

Molar mass is the mass of one mole of a substance, in grams per mole. The tool reads the chemical formula, counts the atoms of each element, and adds up M = Σ (atomic weight × number of atoms) using standard atomic weights stored in the tool, for example H = 1.007, O = 15.999, Ca = 40.078. It understands element symbols (a capital letter plus an optional lower-case letter), subscript numbers written as plain digits, and groups in round or square brackets followed by a multiplier. Element symbols are case-sensitive: Co is cobalt but CO is carbon and oxygen. The result is rounded to two decimals and shown in g/mol, with a breakdown of the atom counts. An unrecognised symbol or bracket mismatch gives an error message.

Common mistakes

• Getting the capital letters wrong: "CO" is carbon monoxide, but "Co" is cobalt, and a lowercase first letter is rejected.
• Leaving out the multiplier of the water in a hydrate: CuSO4·5H2O (or CuSO4.5H2O) means five water molecules; writing CuSO4·H2O counts only one and gives 177.62 g/mol instead of 249.67 g/mol.
• Using Unicode subscript digits such as H₂O rather than ordinary digits (H2O).
• Forgetting the multiplier after a bracket, such as Al2(SO4)3, and leaving out the 3.
• Using the result as an exact isotopic mass; these are average standard atomic weights, so the figure can differ in the last digit from other tables.