🔬 Empirical Formula Calculator
Enter each element’s mass percent (or grams) to get the empirical formula — add the molar mass to find the molecular formula too.
Element and amount (mass % or grams)
Empirical formula
CH2O
30.03 g/mol
| Element | Moles | ÷ smallest | Whole # |
|---|---|---|---|
| C | 3.3303 | 1.000 | 1 |
| H | 6.6468 | 1.996 | 2 |
| O | 3.3315 | 1.000 | 1 |
Divide each element’s amount by its atomic weight, then by the smallest, and scale to whole numbers. 🔒 In your browser.
How the empirical formula calculator works
Each element’s amount is divided by its atomic weight to get moles, then all mole values are divided by the smallest and scaled to whole numbers — that ratio is the empirical formula. If you provide the compound’s molar mass, the tool divides it by the empirical-formula mass to find the whole-number multiple and hence the molecular formula.
The classic “percent to formula” problem, with the mole-ratio table shown. Given 40.0% C, 6.7% H, 53.3% O it returns CH₂O, and with a molar mass of 180 g/mol, C₆H₁₂O₆.
Frequently asked questions
How do I find the empirical formula from percent composition?
Treat the percentages as grams, divide each by the element’s atomic weight to get moles, divide all by the smallest, and round to whole numbers. That whole-number ratio is the empirical formula. This tool shows each step.
What is the difference between empirical and molecular formula?
The empirical formula is the simplest whole-number ratio of atoms (CH₂O); the molecular formula is the actual number in a molecule (C₆H₁₂O₆). The molecular formula is a whole-number multiple of the empirical one.
How do I get the molecular formula?
Divide the compound’s molar mass by the empirical-formula mass to get the multiple, then multiply the subscripts. Enter the molar mass and the tool does it.
Can I use grams instead of percentages?
Yes — enter the measured mass of each element in grams; the method is identical.
What if the ratio isn’t a whole number?
Ratios like 1.5 or 1.33 are scaled up (×2, ×3…) until all are whole numbers — the tool handles this automatically.