Empirical Formula Calculator
The Simplest Ratio Hiding Inside a Compound
Combustion analysis and other lab techniques don't hand you a molecular formula directly — they hand you mass percentages of each element present. The empirical formula is what you get by converting those percentages into the smallest whole-number ratio of atoms, which may or may not match the compound's true molecular formula.
The Method
Divide each mole value by the smallest to get the simplest whole-number ratio
Assuming exactly 100 g of sample lets each percentage be read directly as grams, which simplifies the mole calculation for every element at once.
Where This Calculation Matters
- Combustion analysis — burning an unknown organic compound and measuring CO2 and H2O produced yields elemental percentages that feed directly into this calculation.
- Identifying an unknown compound — the empirical formula is often the first clue toward identifying a substance from elemental analysis data.
- Mineral and material composition — geologists and materials scientists express compound composition using empirical formulas when exact molecular structure isn't the point.
- Quality verification — comparing a measured empirical formula against the expected one flags contamination or synthesis errors.
A Worked Example: Glucose
Glucose (C6H12O6, molar mass 180.156 g/mol) breaks down by mass into 40.00% carbon, 6.71% hydrogen, and 53.28% oxygen. Converting each to moles per 100 g sample and dividing by the smallest value:
| Element | Mass % (of 100 g) | Moles | Ratio to Smallest |
|---|---|---|---|
| C | 40.00 g | 3.331 mol | 1 |
| H | 6.71 g | 6.657 mol | 2 |
| O | 53.28 g | 3.330 mol | 1 |
The ratio 1 : 2 : 1 gives the empirical formula CH2O — note this is not the same as glucose's actual molecular formula, C6H12O6, which is exactly six times larger.
How to Use This Calculator
- Enter each element's symbol in Element 1 Symbol, Element 2 Symbol, and so on, up to four elements.
- Enter the corresponding Mass % for each element.
- Select Calculate to get the simplest whole-number empirical formula.
Related Calculations
If you also know the compound's actual molar mass, the Molecular Formula Calculator scales this empirical formula up to the true molecular formula. To weigh a proposed formula, use the Molar Mass Calculator.