The percent composition calculator finds the mass percentage of each element in a chemical compound. Enter any formula (H2O, C6H12O6, CaCO3) to get a complete elemental breakdown with mass fractions.
Percent Composition Calculator
| Element | Count | Contrib. (g/mol) | % |
|---|
How to Use the Percent Composition Calculator
Enter any chemical formula to see the mass percent of each element. Useful for elemental analysis, verifying compound identity, and empirical formula work.
Example: Water (H₂O)
Molar mass = 18.015 g/mol. H: 2 × 1.008 = 2.016 g/mol → 11.19%. O: 15.999 g/mol → 88.81%. Percentages sum to 100%.
Example: Glucose (C₆H₁₂O₆)
Molar mass = 180.156 g/mol. C: 72.066/180.156 = 40.00%. H: 12.096/180.156 = 6.71%. O: 95.994/180.156 = 53.29%.
Uses in Chemistry
Elemental analysis (combustion analysis) gives mass percent of C, H, N. You can use percent composition to derive the empirical formula. If a compound is 40% C, 6.7% H, 53.3% O: divide by atomic masses to get molar ratios, then find the smallest whole-number ratio: CH₂O (empirical formula of glucose).
FAQ
What is percent composition?
Percent composition is the percentage by mass of each element in a compound. % element = (mass of element in 1 mole / molar mass of compound) × 100%. For H₂O: H is 2×1.008/18.015 = 11.19%, O is 15.999/18.015 = 88.81%. These percentages always sum to 100%.
How is percent composition used in chemistry?
Percent composition helps determine empirical formulas from experimental data, verify purity of compounds, calculate elemental analysis results, and identify unknown compounds. If you burn a compound and measure CO₂ and H₂O produced, you can calculate percent C, H, and (by difference) other elements.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted.
What is the difference between empirical and molecular formulas?
The empirical formula shows the simplest whole-number ratio of elements. The molecular formula shows the actual number of atoms. Glucose (C₆H₁₂O₆) has empirical formula CH₂O. H₂O₂ (hydrogen peroxide) has empirical formula HO. You can find the molecular formula if you know the molar mass.