Empirical Formula Calculator
List each element with its mass or percentage, one per line. You get the simplest whole number ratio, and the molecular formula if you add the molar mass.
One element per line: a symbol, then the mass in grams or the percentage. Percentages are treated as grams in a 100 g sample.
Worked examples
Rust
Fe 69.94, O 30.06
Fe2O3
Ratio 1 to 1.5, doubled.
Glucose
C 40.0, H 6.71, O 53.29 and molar mass 180.16
CH2O, so C6H12O6
180.16 / 30.03 is 6.
About Empirical Formula Calculator
The empirical formula shows the simplest whole number ratio of atoms in a compound. To find it from an analysis, convert each element's mass to moles by dividing by its atomic weight, then divide all the mole values by the smallest one. If the results are close to whole numbers you are done. If not, multiply them all by 2, 3 or 4 until they are, for example a ratio of 1.5 becomes 3 when doubled.
The empirical formula may not be the molecular formula. Glucose is C6H12O6 but its empirical formula is CH2O. To find the molecular formula, divide the compound's molar mass by the mass of the empirical formula and multiply every subscript by the answer. Enter the molar mass if you have it. The page shows the working in a table, with the moles, the ratio to the smallest and the final whole number for each element, so you can follow every step.
How to use Empirical Formula Calculator
- Type one element per line: its symbol, then the mass in grams or the percentage.
- Optionally enter the molar mass of the compound.
- Read the empirical formula and the molecular formula if a molar mass was given.
- Check the table to see the ratios at each step.
Common uses
- Combustion analysis and percentage composition questions
- Identifying an unknown compound from lab data
- Checking a formula against analysis results
- Exam practice on empirical and molecular formulae
Frequently asked questions
How do I find an empirical formula?
Convert masses to moles, divide by the smallest number of moles, and multiply to reach whole numbers. The whole numbers are the subscripts.
Can I use percentages?
Yes. Treat the percentages as grams in a 100 gram sample. They should add to about 100 if all the elements are listed.
What if the ratios are not whole numbers?
Look for a simple multiplier. 1.5 needs 2, 1.33 needs 3 and 1.25 needs 4. The page tries multipliers up to 4 and tells you if none fits.
How do I get the molecular formula?
Divide the molar mass by the empirical formula mass to get a whole number, then multiply each subscript by it. 180 divided by 30 is 6, so CH2O becomes C6H12O6.