🔬 Percent Composition Calculator
Find what percentage of a compound’s total mass comes from a specific element by entering the element’s mass contribution and the compound’s molar mass.
What Is Percent Composition?
Percent composition tells you what fraction of a compound’s total mass is contributed by a particular element. It is widely used to verify chemical formulas, check purity, and convert between mass and molar quantities in stoichiometry problems.
The Formula
Percent composition by mass is calculated as: % element = (total mass of that element in the formula ÷ molar mass of the compound) × 100. The ‘mass of element in formula’ is the atomic mass of the element multiplied by however many atoms of it appear in the compound’s chemical formula.
- Enter the combined mass contributed by the element (atomic mass × number of atoms) in g/mol.
- Enter the molar mass of the whole compound in g/mol.
This calculator is intended for general chemistry education and homework-checking purposes; always verify formula subscripts and atomic masses against a reliable periodic table.