Percent Composition Calculator
Compute each element’s mass percentage in a compound from atom counts and atomic masses, plus total molar mass for context.
Inputs
Equation Preview
Helping Notes
Molar mass equals the sum of each element’s atomic mass multiplied by its atoms present in one molecule.
Percent of an element equals its mass contribution divided by compound molar mass, then multiplied by one hundred.
Use whole-number atom counts derived from the molecular formula; decimals do not apply to discrete atoms.
Results
Constructed Formula
Molecular Weight (g/mol)
Mass of Each Element (g per mole)
Percent Composition by Mass (%)
What Is Percent Composition Calculator?
The Percent Composition Calculator determines the mass percentage of each element in a chemical compound. By parsing a chemical formula (including parentheses and hydrate dots), it multiplies each element’s atomic weight by its subscript, sums the contributions to obtain the compound’s molar mass, and then divides each element’s contribution by the total. The result is a neat breakdown that helps with lab calculations, stoichiometry, reporting standards, and quality control. You can also pair the output with a chosen sample mass to estimate grams of each element present. This saves time, eliminates manual arithmetic errors, and keeps your work consistent across multiple compounds.
About the Percent Composition Calculator
Built for reliability and clarity, the calculator supports: standard element symbols, nested groups (e.g., Al2(SO4)3), and hydrates using dot notation (e.g., CuSO4·5H2O). It uses tabulated atomic weights to compute a compound molar mass and then outputs element‑by‑element percentages that typically sum to ~100% (minor rounding may occur). Optional fields let you specify a sample mass so the tool can convert mass percent into grams per element. For empirical‑formula work, you can use the reported percentages to derive simplest whole‑number ratios. Clear, responsive math rendering ensures formulas are easy to read on any screen.
How to Use this Percent Composition Calculator
1) Enter a chemical formula (e.g., C6H12O6, NaCl, or CuSO4·5H2O). 2) Choose decimals for reporting. 3) (Optional) Enter a sample mass to obtain grams of each element. 4) Submit to compute the molar mass and the mass percent of every element. 5) Review the totals, copy the table, or export for lab notes. If you need an empirical formula, convert the percentages to moles by dividing by atomic weights and normalize to the smallest value.
Examples Using the Percent Composition Calculator
• Water (H2O): H ≈ 11.19%, O ≈ 88.81%.
• Sodium chloride (NaCl): Na ≈ 39.34%, Cl ≈ 60.66%.
• Calcium carbonate (CaCO3): Ca ≈ 40.04%, C ≈ 12.00%, O ≈ 47.96%.
• Iron(III) oxide (Fe2O3): Fe ≈ 69.9%, O ≈ 30.1%.
Core Formulas (rendered responsively)
Compound molar mass equals the sum of each element’s stoichiometric count times its atomic weight.
Mass percent of element i.
Mass of element i in a given sample mass.
Water percentage in a hydrate (e.g., \cdot x\,H2O).
Empirical‑formula workflow: convert mass fractions to moles and normalize to the smallest to get whole‑number ratios.
FAQs
What is percent composition used for?
It shows how much of each element is present by mass, supporting stoichiometry, purity checks, and reporting in lab documentation.
Do the percentages always sum to exactly 100%?
They should sum very close to 100%. Small discrepancies arise from rounding of atomic weights and display precision settings.
How do I enter hydrates correctly?
Use a centered dot: CuSO4·5H2O. The calculator treats the water as part of the formula mass and reports its percentage.
Can the tool handle nested groups and parentheses?
Yes. Formulas like Al2(SO4)3 are parsed by multiplying subscripts through each grouped term before summing masses.
How do I get grams of each element from the percentages?
Enter a sample mass. Each element’s grams equals percent divided by 100 times the sample mass, using the formula shown above.
What’s the difference between percent composition and empirical formula?
Percent composition is a mass breakdown; the empirical formula is the simplest integer mole ratio derived from those percentages.
Why don’t my totals match a textbook exactly?
Atomic weights vary slightly by source and significant figures. Adjust precision to align with your reference table if needed.
Does this support isotopic compositions?
Results use standard atomic weights. For isotopic mixtures, substitute the relevant isotopic masses to tailor the calculation.
Can it compute mole fraction or mass fraction?
The output is mass percent. You can convert to mass fraction by dividing by 100; mole fractions require converting to moles first.
Does this work for mixtures or solutions?
It assumes a pure compound. For mixtures, calculate each component’s contribution and weight them by proportion to get overall percentages.
How many decimal places should I use?
Match your lab or reporting standard. Two decimals are common; more precision may be useful for research or high‑purity materials.