Empirical formula calculator
Type each element with its percent or mass, like C 40, H 6.71, O 53.29, to get the simplest whole-number ratio of atoms.
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How to use it
- Enter elements with percent or grams.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Moles of each element = mass ÷ atomic weight; divide all by the smallest, then multiply by the smallest whole number (1 to 10) that brings every ratio within 0.1 of an integer.
Example
Inputs: Elements with percent or grams = C 40, H 6.71, O 53.29. Result: Empirical formula: CH2O; Empirical formula mass: 30.026 g/mol.
C 40, H 6.71, O 53.29
CH2O
Limits and caveats
- Imprecise lab data can give a wrong formula; ratios within 0.1 of a whole number are accepted.
- Elements appear in the order you typed them, and the true molecular formula needs the molar mass as well.
Questions about this tool
Do I enter percentages or grams?
Either works, because only the ratio between moles matters.
Why Fe2O3 and not FeO1.5?
A 1 to 1.5 ratio is multiplied by 2 to make whole numbers, giving Fe2O3.
What if oxygen is not given?
If oxygen is the remainder, subtract the other percentages from 100 and enter the result for O.