Molar Mass Calculator, Formula & Compound List

Molar mass is calculated by adding the atomic masses of all atoms in a compound.

M = Σ (atomic mass × number of atoms)

CO₂ → (1 × 12.01) + (2 × 16.00)

Ca(OH)₂ → (1 × Ca) + (2 × O) + (2 × H)

Parentheses indicate that all atoms inside the group are multiplied by the subscript outside.

Find the element's atomic mass on the periodic table. That value is the molar mass in g/mol. For example, carbon has an atomic mass of 12.01, so its molar mass is 12.01 g/mol.

Remember the seven diatomic elements in their natural form: H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂.

Add the masses of all atoms in the formula. Multiply each element's atomic mass by its atom count, including any counts affected by subscripts and parentheses.

Example: NaCl → (1 × 22.99) + (1 × 35.45) = 58.44 g/mol. Example: FeCl₂ → (1 × 55.85) + (2 × 35.45) = 126.75 g/mol.

For grouped formulas such as Zn(NO₃)₂, multiply atoms inside parentheses by the outside subscript before adding each element's total mass.