Empirical Formula Calculator

What This Calculator Does

This calculator determines a compound’s empirical formula — the simplest whole-number ratio of atoms of each element in the compound — from the mass (or percent composition) of each element present.

The Formula

The method has three steps: first, convert each element’s mass to moles using moles = mass ÷ atomic weight. Second, divide every mole value by the smallest one to get a mole ratio. Third, if any ratio isn’t close to a whole number, multiply all ratios by the same small integer (2, 3, 4…) until they are, then round to get the empirical formula’s subscripts.

A Few Notes

• If you have percent composition instead of mass, you can enter the percentages directly — treating them as if they were grams out of a 100 g sample gives the identical ratio.
• The empirical formula shows the simplest ratio only; the compound’s true (molecular) formula may be a whole-number multiple of it.
• This tool is provided for general educational and reference purposes.