Find the empirical formula of a compound from its percent composition or the mass of each element, with every step shown. Add the compound’s molar mass and this free calculator also gives the molecular formula.
How to find an empirical formula
- Assume 100 g of compound so percentages become grams (or use the masses you measured).
- Convert each mass to moles by dividing by the atomic mass.
- Divide every mole value by the smallest one.
- If any ratio isn’t close to a whole number (for example 1.5 or 1.33), multiply all of them by 2, 3, 4… until they are.
- For the molecular formula, divide the molar mass by the empirical formula mass and multiply the subscripts by that whole number.
Frequently asked questions
What is an empirical formula?
The simplest whole-number ratio of atoms in a compound. Glucose (C₆H₁₂O₆) and acetic acid (C₂H₄O₂) both have the empirical formula CH₂O.
How do I find the empirical formula from percentages?
Treat each percent as grams, convert to moles, divide by the smallest number of moles and round to whole numbers, multiplying through if you get ratios like 1.5.
How do I get the molecular formula?
Divide the compound’s molar mass by the empirical formula mass, then multiply every subscript by that whole number. Enter the molar mass and the calculator does it.
What if my percentages don’t add to 100?
Small differences from rounding or experimental error are fine. If oxygen wasn’t measured, it is often the missing remainder: add it as O with 100 minus the total.
Related tools
Free educational tool by HawkInc. Results are calculated in your browser and rounded for display; check critical work by hand or with a second method.