Empirical Formula Calculator

This calculator determines the empirical formula of a compound, the simplest whole-number ratio of its atoms, from the percentage composition or masses of its elements. The empirical formula is a fundamental result in chemistry: it tells you the relative numbers of each kind of atom in a substance, reduced to the lowest terms. Glucose, for instance, has the molecular formula C6H12O6 but the empirical formula CH2O, because the atoms are in the ratio one to two to one. Chemists determine empirical formulas from experimental data, typically the percentage by mass of each element found by analysis, which is the first step in identifying an unknown compound. The method is a clear sequence: treat the percentages as grams in a 100 gram sample, convert each element's mass to moles by dividing by its molar mass, then divide all the mole figures by the smallest to get the ratio, and finally scale up to the nearest whole numbers. It is reliable but tedious by hand, with plenty of room for arithmetic slips. This tool does it automatically. You enter each element's symbol, its percentage or mass, and its molar mass, for up to three elements, and the calculator works out the mole ratio and presents the empirical formula. It shows the mole ratios too, so you can follow the logic. The results update as you type. Use it for chemistry homework, for interpreting analytical data, or to check your working. A note: the empirical formula gives the ratio, not the actual molecule; to get the molecular formula you also need the compound's molar mass. The calculation rounds the ratio sensibly to the nearest small whole numbers.

Enter percent by mass (or grams) and molar mass for each element. Leave an element blank to ignore it. Gives the ratio, not the molecular formula. Rounded sensibly.