Percent Composition Calculator

Percent composition tells you what fraction of a compound's mass comes from each element — the first thing an analyst checks against a new synthesis. Give the number of atoms of the element, its atomic mass, and the compound's molar mass to get its mass percent.

Percent Composition Calculator

$\%\ element = \frac{atoms \times atomic\ mass}{molar\ mass} \times 100$

Solve for

Atoms of element per formula unit (atoms)

Unit

Atomic mass of element (A)

Unit

Molar mass of compound (M)

Unit

Result unit

How to interpret the result

Worked check: hydrogen in water — (2 × 1.008 / 18.015) × 100 = 11.19%. The percents of all elements in a formula must add to 100%.

Assumptions

Atomic and molar masses use the same mass unit (g/mol)
The formula unit is correct and complete