Empirical Formula Calculator
Determine empirical and molecular formulas from element mass percentages or experimental mass data with step-by-step solutions.
What Is an Empirical Formula?
The empirical formula shows the simplest whole-number ratio of atoms in a compound. It does not always match the molecular formula. For example, glucose has molecular formula C6H12O6 but empirical formula CH2O.
From Mass Percentages
Assume a 100 g sample. Convert each element percentage to grams, divide by atomic mass to get moles, then divide all mole values by the smallest mole count to obtain the simplest ratio.
From Experimental Mass
When you have measured masses in grams, divide each mass by atomic mass, normalize by the smallest mole value, and round to whole-number subscripts.
Molecular Formula
If the compound molar mass is known, divide it by the empirical formula mass. The nearest whole-number multiplier gives the molecular formula subscripts.
Related tools: use the Molecular Weight Calculator for formula mass checks and the Molarity Calculator for solution concentration work.
Frequently Asked Questions
What is the difference between empirical and molecular formulas?
The empirical formula uses the smallest whole-number atom ratio. The molecular formula shows the actual number of atoms per molecule and is always a whole-number multiple of the empirical formula.
Why must mass percentages sum to 100%?
Percent composition describes how mass is distributed across elements in a pure sample. If the total is not close to 100%, the input data is incomplete or inconsistent.
Can two different compounds share the same empirical formula?
Yes. Formaldehyde (CH2O) and glucose (C6H12O6) share empirical formula CH2O, but glucose has six times as many atoms per molecule.
How do I choose the right atomic masses?
Use standard periodic-table atomic weights in g/mol. This calculator uses common IUPAC values for elements such as C, H, O, N, S, Fe, and Na.
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