Empirical Formula Calculator
Find a compound's empirical formula from the mass percentage of each element, using moles and the smallest whole-number ratio.
Mole ratio (approx.)
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Moles per 100 g —
If the ratio doesn't look like whole numbers, multiply all values by 2, 3, or 4 until they do.
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How it works
Moles of each element = mass% ÷ atomic mass; divide all by the smallest to get the ratioFrequently Asked Questions
How do I find an empirical formula from percent composition?
Treat the percentages as grams (assume 100 g sample), divide each by its atomic mass to get moles, then divide every mole value by the smallest one to get a whole-number ratio — a compound that's 40.0% C, 6.7% H, 53.3% O gives a 1:2:1 ratio, or CH₂O.
What if the ratio isn't a whole number?
Multiply all values by a small integer (2, 3, 4) until they round cleanly to whole numbers — a ratio like 1 : 1.5 becomes 2 : 3 when doubled. Small rounding errors from real lab data are normal.
Is empirical formula the same as molecular formula?
Not always — the empirical formula is the simplest whole-number ratio (like CH₂O for glucose), while the molecular formula is the true count of atoms (C₆H₁₂O₆ for glucose, 6× the empirical ratio). You need the compound's molar mass to find the molecular formula from the empirical one.