Percent Composition Calculator

Calculate the mass percent of an element in a compound.

Percent Composition Calculator

Calculate the mass percent of an element in a compound.

Formula
% Composition = (mass of element / molar mass of compound) x 100
What is This Tool?

Percent composition tells you the percentage by mass of each element in a chemical compound. It is calculated by dividing the total mass contribution of an element in one mole of the compound by the molar mass of the compound, then multiplying by 100.

Formula
% by mass = (n x atomic mass of element / molar mass of compound) x 100 Where n = number of atoms of that element in the formula
Worked Examples

1. Calcium in CaCO3

Given: Ca mass = 40.08 g/mol, CaCO3 molar mass = 100.09 g/mol

% Ca = (40.08 / 100.09) x 100

% Ca = 40.04%

Result: 40.04% calcium

2. Oxygen in H2O

Given: O mass = 16.00 g/mol, H2O molar mass = 18.015 g/mol

% O = (16.00 / 18.015) x 100

% O = 88.81%

Result: 88.81% oxygen

Frequently Asked Questions