Empirical Formula Calculator

An empirical formula is the simplest whole number ratio of atoms in a compound. For example glucose, C6H12O6, has the empirical formula CH2O, and hydrogen peroxide, H2O2, reduces to HO.

Treat the percentages as grams in a 100 gram sample, divide each by its atomic mass to get moles, divide every value by the smallest, then scale to whole numbers. Choosing Percent by mass does exactly this.

The tool multiplies every ratio by the smallest integer that makes them whole, up to 6. So 1.5 is doubled and 1.33 is tripled, turning 69.9% Fe and 30.1% O into Fe2O3 rather than FeO1.5.

Yes. Choose Mass in grams and type the measured mass of each element. The math is identical, since moles are mass divided by atomic mass either way. For example 24 g C and 6 g H give CH3.

As many as you need. Click Add element to append rows and Remove to drop them, though at least one row always stays. Element order is preserved, so the formula follows the order you enter, such as C then H then O.

All 118 elements by their standard symbol, case sensitive, so C, Cl, Fe and Na work but lowercase c or misspellings are rejected as an unknown symbol. Atomic masses follow IUPAC conventional values.

The tool accepts a scaled ratio as whole when it lands within 0.12 of an integer, which absorbs rounding in textbook percentages. Rough or inconsistent percentages can push a value past that window and force a larger multiplier, so use accurate figures.

Not always. The molecular formula is a whole number multiple of the empirical formula. Glucose is six times CH2O. To find the molecular formula you also need the compound's molar mass, which this tool does not use.

Yes. Everything runs in your browser with a built-in table of atomic masses, so nothing you enter is sent to a server. It works offline once the page has loaded.