Enter a compound formula to see its molar mass, atom counts, mass contribution, and percent composition by element.
Cross-check a chemical formula with molar mass, detected elements, rendered composition percentages and a 100% mass-balance audit.
The calculator first totals the formula’s molar mass, then divides each element’s mass contribution by that total. Parentheses and subscripts change atom counts before the percentages are calculated. The element percentages should add to about 100%, with small differences possible from displayed rounding.
Use the tool first, then apply these checks to verify the inputs, interpret the result, and hand it off without displacing the primary workflow.
Percent composition is only as correct as the parsed formula. Check element symbols, subscripts, grouping, hydrates, and any notation the parser supports. A typographical formula can still produce internally consistent percentages for the wrong compound.
Each element’s contribution is its atomic mass multiplied by its atom count. The element contributions should sum to the total molar mass, and the displayed percentages should sum to approximately 100 percent subject to rounding. Those checks catch many parsing or transcription mistakes.
Formula-based mass percentages describe an ideal chemical formula. A real sample can contain solvent, water, impurities, mixtures, or incomplete reaction products. Do not interpret the theoretical percent as an assay or purity result without measurement evidence.
Published atomic weights can be intervals or rounded reference values. Small differences in the atomic masses or number of displayed decimals can shift the final percentages slightly. State the convention when comparing answers from different textbooks, software, or laboratory systems.
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