🧮 Percent Composition Calculator
Determine elemental mass percentages from any chemical formula.
Supports nested parentheses and integer subscripts.
How to Use This Calculator
Write the chemical formula
Enter the empirical or molecular formula using proper element symbols and subscripts. Include parentheses for polyatomic groups as needed.
Run the calculation
The parser counts each atom, multiplies by modern atomic weights, and obtains the overall molar mass.
Review the elemental table
Inspect the mass contribution and percent composition for each element. Use the data to construct composition charts or verify homework.
Apply the results
Use the percentages in stoichiometry, gravimetric analysis, or to confirm empirical formula calculations.
Formula
% Element = (mass contribution of element / total molar mass) × 100
Mass contribution is calculated by multiplying the number of atoms of an element in the formula by its atomic mass. Summing all contributions yields the compound's molar mass, which serves as the denominator for percent calculations.
Example: Magnesium hydroxide, Mg(OH)2
Molar mass = 24.305 + (2 × 15.999) + (2 × 1.008) = 58.319 g/mol
Percent Mg = 24.305 / 58.319 × 100 = 41.67%
Percent O = 31.998 / 58.319 × 100 = 54.86%
Percent H = 2.016 / 58.319 × 100 = 3.46%
Full Description
Percent composition quantifies how much of a compound's mass comes from each constituent element. It is fundamental in analytical chemistry, pharmaceutical formulation, and environmental monitoring. This calculator automates tedious manual calculations by parsing complex formulas (including hydrates and coordination compounds) and returning precise mass percentages based on contemporary atomic weights.
Use it to confirm laboratory measurements, design gravimetric experiments, or illustrate the relationship between molecular formulas and mass contributions in lectures. Because results include both the molar mass and individual contributions, the tool doubles as a molar mass calculator and percent composition explainer.
Who benefits?
- Students: Check homework and develop intuition for composition problems.
- Laboratory chemists: Validate reagent purity and formulation data.
- Quality control analysts: Document composition in compliance reports.
- Educators: Demonstrate how molecular structure affects mass percentages.
- Environmental scientists: Estimate elemental contributions in pollutants or aerosols.
Key advantages
- ✅ Accurate atomic weights: Uses modern values to four decimal places.
- ✅ Robust parser: Handles parentheses and nested groups common in inorganic compounds.
- ✅ Comprehensive output: Provides mass contributions, percentages, and molar mass in one view.
- ✅ Time saver: Eliminates repetitive calculations during labs or assignments.
- ✅ Mobile friendly: Works on tablets and phones for on-the-go reference.
Frequently Asked Questions
Does the calculator support hydrates?
Yes. Enter hydrates using parentheses, e.g., CuSO4(H2O)5. Water molecules will be included in the percent composition automatically.
Why don't percentages add up to exactly 100%?
Minor rounding to two decimal places can cause totals like 99.99% or 100.01%. Increase precision if you require exact sums.
Can I calculate percent composition for mixtures?
The tool is designed for pure compounds. For mixtures, compute percent composition for each component separately and weight by mixture proportions.
How often are atomic masses updated?
Values align with IUPAC standard atomic weights (2019). Update the mass table in the code if future revisions are released.
Can the results help find empirical formulas?
Yes. You can reverse the process by using percent composition data to derive empirical formulas, making this tool ideal for cross-checking your calculations.