Empirical Formula Calculator

Calculate the simplest whole-number ratio of elements in a compound from their masses or mass percentages. Enter each element, atomic mass, and measured amount to get the empirical formula with calculation steps.

Instant Result Chemistry Tool Mole Ratio Steps

Calculate Empirical Formula

Add at least two elements and enter their atomic masses and sample masses or percentages.

How to enter data: If you have percentage composition, simply enter each percentage in the Amount field. Percentages can be treated as grams in a hypothetical 100 g sample.

Element Symbol

Atomic Mass

Mass / Percentage

Empirical Formula

The subscripts represent the simplest whole-number mole ratio of the elements entered.

Element	Amount	Atomic Mass	Moles	Ratio	Whole Ratio

Chemistry Guide

What Is an Empirical Formula?

An empirical formula shows the simplest whole-number ratio of atoms of each element in a chemical compound. It does not necessarily show the actual number of atoms in one molecule.

For example, a molecular formula may contain atom counts that can be reduced by a common factor. The empirical formula represents that reduced ratio.

Important: An empirical formula represents the simplest ratio. A molecular formula may be the same as the empirical formula or a whole-number multiple of it.

Calculation Method

Empirical Formula Calculation

The first step is to convert the mass of each element into moles. This is done by dividing the element's mass by its atomic mass.

Moles = Element Mass ÷ Atomic Mass Then divide all mole values by the smallest mole value.

Simple Process

How to Calculate an Empirical Formula

Enter Elements

Enter the chemical symbol for each element present in the compound.

Convert to Moles

Divide each element's mass or assumed percentage mass by its atomic mass.

Find Mole Ratios

Divide every mole value by the smallest number of moles in the set.

Get Formula

Convert the ratios into the smallest reasonable whole numbers and use them as subscripts.

Example

Empirical Formula Example

Consider a compound containing approximately 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. For percentage data, imagine a 100 g sample, so the percentages correspond numerically to masses in grams.

Element	Mass	Atomic Mass	Approx. Moles
Carbon (C)	40.0 g	12.011	3.33
Hydrogen (H)	6.7 g	1.008	6.65
Oxygen (O)	53.3 g	15.999	3.33

Dividing these values by the smallest mole value gives an approximate ratio of 1 : 2 : 1. The empirical formula is therefore CH₂O.

Key Difference

Empirical Formula vs Molecular Formula

Feature	Empirical Formula	Molecular Formula
Meaning	Simplest whole-number atom ratio	Actual number of atoms in a molecule
Can Be Reduced?	Already in simplest form	May sometimes be reducible
Example	CH₂O	C₆H₁₂O₆
Relationship	Basic ratio	Whole-number multiple of empirical formula

Frequently Asked Questions

Empirical Formula Calculator FAQs

What is the empirical formula?

The empirical formula represents the simplest whole-number ratio of the atoms or moles of each element in a compound.

How do you calculate an empirical formula?

Convert each element's mass to moles, divide all mole values by the smallest mole value, and convert the resulting ratios into the smallest reasonable whole numbers.

Can I calculate an empirical formula from percentages?

Yes. For mass percentages, you can assume a 100 gram sample. This means each percentage has the same numerical value as the corresponding mass in grams.

Why do we divide by atomic mass?

Dividing mass by atomic or molar mass converts the measured mass into an amount in moles. Mole amounts can then be compared to determine the elemental ratio.

Why divide all moles by the smallest value?

Dividing by the smallest mole value normalizes the amounts and reveals the relative mole ratio between the elements.

What if the mole ratios are decimals?

Some ratios are naturally close to fractions such as 1.5, 1.33, or 1.25. In those cases, all ratios can be multiplied by a small integer to obtain the simplest reasonable whole-number ratio.

Is empirical formula the same as molecular formula?

Not always. The empirical formula is the simplest ratio, while the molecular formula gives the actual number of atoms in a molecule. The molecular formula can be a whole-number multiple of the empirical formula.

Can the empirical and molecular formulas be identical?

Yes. They are identical when the molecular formula is already expressed in the simplest whole-number ratio.