Chemistry
Percent Composition Calculator
Find the mass percentage an element contributes to a compound from its atomic mass, atom count and the compound's molar mass.
Your inputs
Change any value to update the result instantly.
Percent by mass
11.191 %
Mass of this element per mole
2.016 g
Mass of all other elements
15.999 g
Remaining composition
88.809 %
What this calculator does
Calculates the mass percentage contributed by one element within a compound.
What your result means
The share of the compound's mass made up by the chosen element, per mole of compound.
Formula and working
% element = (n × A ÷ M_compound) × 100
- 1
Collect the inputs
Atoms of the element per formula unit (n) = 2; Atomic mass of the element (A) = 1.008 g/mol; Molar mass of the compound (M) = 18.015 g/mol
- 2
Apply the formula
% element = (n × A ÷ M_compound) × 100
- 3
Result
Percent by mass = 11.191 %
Frequently asked questions
Symbols and assumptions
- n
- Atoms of the element per formula unit
- A
- Atomic mass of the element
- M
- Molar mass of the compound
- • Atom count and atomic mass refer to one formula unit of the compound.
- • The compound's molar mass is correct.
Sources and review
Reviewed 2026-09-22 · Next review 2027-09-22
- • Does not parse chemical formulas; you enter the atom count and masses yourself.
Important limitation
This is an educational estimate based only on the values and formula shown. Verify current rates, rules, units, and professional standards before relying on the result. It is not personalized financial or investment advice.
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