Percent Composition Calculator
Find the mass percent of each element in a chemical formula.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Enter a chemical formula (e.g., H2O, C6H12O6, Ca(OH)2). The calculator parses the formula, multiplies each element count by its atomic mass, and divides by the total molar mass to give the mass percent of each element.
About the Percent Composition Calculator
Percent composition tells you what fraction of a compound, by mass, comes from each element. It is a fundamental concept in analytical chemistry that connects chemical formulas to experimental measurements from techniques like combustion analysis, mass spectrometry, and elemental analysis.
Frequently Asked Questions
How is percent composition calculated?
Divide the total mass of each element in one formula unit by the molar mass of the compound, then multiply by 100. For H2O: H = 2(1.008)/18.015 x 100 = 11.19%, O = 15.999/18.015 x 100 = 88.81%.
Should percent composition add up to 100%?
Yes. The percent composition of all elements in a compound must sum to exactly 100% (with minor rounding differences). If your total is significantly off, check the formula for errors.
What is percent composition used for?
Percent composition is used to verify the identity of compounds, check purity, and as input for empirical formula determination. It connects a formula to measurable laboratory quantities.