Empirical Formula Calculator
Calculate the empirical formula from percent composition data.
Enter up to 5 elements with their mass percentages and get the simplest whole-number ratio.
The empirical formula shows the simplest whole-number ratio of atoms in a compound. It may or may not be the same as the molecular formula.
How to determine it from percent composition:
- Assume 100 grams of sample → percentages become grams directly
- Convert grams to moles: n = mass / atomic mass
- Divide all mole values by the smallest one to get ratios
- Round to nearest whole numbers (if close to 0.5, multiply all by 2)
Example: Compound with 40.00% C, 6.71% H, 53.29% O
- C: 40.00/12.011 = 3.330 mol
- H: 6.71/1.008 = 6.657 mol
- O: 53.29/15.999 = 3.331 mol
- Divide by smallest (3.330): C:H:O = 1:2:1
- Empirical formula: CH₂O (formaldehyde, sugars, etc.)
Molecular formula from empirical formula:
Molecular formula = (Empirical formula)_n
n = Molar mass / Empirical formula mass
For CH₂O (emp. mass = 30.03):
- Glucose (M = 180.16): n = 180.16/30.03 = 6 → C₆H₁₂O₆
- Formaldehyde (M = 30.03): n = 1 → CH₂O (empirical = molecular)
- Acetic acid (M = 60.05): n = 2 → C₂H₄O₂
Common empirical formulas vs molecular formulas:
| Empirical | Molecular |
|---|---|
| CH₂O | Glucose C₆H₁₂O₆ |
| CH | Benzene C₆H₆, Ethyne C₂H₂ |
| CH₂ | Ethylene C₂H₄, Cyclohexane C₆H₁₂ |
| HO | Hydrogen peroxide H₂O₂ |
| NaCl | NaCl (empirical = molecular for ionic compounds) |
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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