Empirical Formula Calculator
Find the empirical formula of a compound from its percent composition or element masses, and its molecular formula if you know the molar mass.
Calculate the Empirical Formula
Enter each element in the compound along with its mass or percent composition. Leave any value as a percentage and treat the sample as 100g, or enter actual masses from an experiment.
Compound Composition
Enter the elements present and their amounts
Formula Result
Empirical formula and mole ratio breakdown
Common Empirical Formula Examples
A few well-known compounds where the empirical formula differs from the molecular formula.
| Compound | Molecular Formula | Empirical Formula |
|---|---|---|
| Glucose | C6H12O6 | CH2O |
| Acetylene | C2H2 | CH |
| Benzene | C6H6 | CH |
| Hydrogen Peroxide | H2O2 | HO |
| Ethane | C2H6 | CH3 |
| Water | H2O | H2O |
Empirical Formula FAQ
Everything you need to know about calculating empirical and molecular formulas.
An empirical formula shows the simplest whole-number ratio of atoms of each element in a compound. For example, the empirical formula of glucose is CH2O, even though its molecular formula is C6H12O6.
Assume a 100g sample so each percentage becomes a mass in grams. Divide each element’s mass by its atomic mass to get moles, then divide every mole value by the smallest one to get a ratio. Round the ratios to the nearest whole numbers to get the empirical formula subscripts.
The empirical formula gives the simplest whole-number ratio of atoms, while the molecular formula gives the actual number of atoms of each element in one molecule of the compound. The molecular formula is always a whole-number multiple of the empirical formula.
Divide the compound’s molar mass by the empirical formula mass to get a whole number multiplier, then multiply every subscript in the empirical formula by that multiplier to get the molecular formula.
This usually happens when a ratio lands near a fraction like 0.5, 0.33, or 0.25. Multiplying every ratio by 2, 3, or 4 (whichever clears the fraction) before rounding will usually produce clean whole numbers.