Enter each element, its atomic mass, and its percentage or mass. The calculator converts the values to moles and finds the simplest whole-number formula.
Enter correct atomic masses and positive values. Percentages should total about 100%. Small rounding differences are allowed.
An empirical formula shows the simplest whole-number ratio of atoms in a compound. A molecular formula shows the actual number of atoms of each element in one molecule.
Multiplier (n) = Molecular molar mass ÷ Empirical formula mass
Molecular formula = empirical formula with every subscript multiplied by n.
| Feature | Empirical formula | Molecular formula |
|---|---|---|
| Meaning | Smallest whole-number atom ratio | Actual number of atoms in a molecule |
| Glucose example | CH₂O | C₆H₁₂O₆ |
| Needs molar mass? | Not always | Usually, to derive it from the empirical formula |
| Can both be the same? | Yes | Yes, when the multiplier is 1 |
A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. Assume a 100 g sample. The masses are 40.0 g carbon, 6.7 g hydrogen, and 53.3 g oxygen.
| Element | Mass (g) | Atomic mass | Moles (approx.) | Ratio |
|---|---|---|---|---|
| C | 40.0 | 12.011 | 3.33 | 1 |
| H | 6.7 | 1.008 | 6.65 | 2 |
| O | 53.3 | 15.999 | 3.33 | 1 |
The simplest ratio is 1:2:1. Therefore, the empirical formula is CH₂O.
The empirical formula is CH₂O and the molecular molar mass is 180.16 g/mol.
The molecular formula is C₆H₁₂O₆.
Water has the molecular formula H₂O. The ratio of hydrogen to oxygen is already 2:1, the smallest whole-number ratio. Its empirical formula is also H₂O.
An empirical formula gives the simplest whole-number ratio of atoms in a compound. For example, CH₂O is the empirical formula of glucose.
A molecular formula gives the actual number of each type of atom in one molecule. Glucose has the molecular formula C₆H₁₂O₆.
Yes. They match when the molecular formula is already in its simplest whole-number ratio, as with water, H₂O.
Assume a 100 g sample. Treat each percentage as grams, then divide each mass by the element’s atomic mass.
Multiplying every ratio by the same number can turn fractional ratios into whole numbers without changing the relative proportions.
You can usually find the empirical formula, but you cannot determine the unique molecular formula from the empirical formula alone. You need the molecular molar mass or other suitable information.
Disclaimer: This educational calculator uses the atomic masses you enter and rounded numerical methods. Check your working and follow your course or laboratory instructions.
Zain Bin Shabbir is a content creator and website publisher with 2 years of experience in SEO, web content, and practical online tools. He focuses on creating clear, useful, and user-friendly resources that simplify everyday calculations.
Guides that go deeper into this topic
