Empirical Formula Calculator – Find Empirical Formula from Percent Composition

Find the empirical formula of any compound using our free empirical formula calculator. Enter percent composition or mass of each element to instantly get the simplest whole-number ratio. Great for general and organic chemistry students.

What is an Empirical Formula?

The empirical formula shows the simplest whole-number ratio of atoms in a compound. It differs from the molecular formula, which shows the actual number of atoms. For example, glucose has molecular formula C₆H₁₂O₆ but empirical formula CH₂O.

Steps to Find Empirical Formula

Convert percent composition to grams (assume 100 g sample)
Convert grams to moles using atomic masses
Divide all mole values by the smallest mole value
Multiply by integers if needed to get whole numbers
Write the formula using these ratios as subscripts

Example Calculation

A compound contains 40.0% C, 6.7% H, and 53.3% O by mass.

In 100 g: 40.0 g C, 6.7 g H, 53.3 g O
Convert to moles: C = 40.0/12.01 = 3.33 mol, H = 6.7/1.008 = 6.65 mol, O = 53.3/16.00 = 3.33 mol
Divide by smallest (3.33): C = 1, H = 2, O = 1
Empirical formula: CH₂O

Percent Composition Chart

Enter values and calculate to see the chart

Empirical vs Molecular Formula

Compound	Molecular Formula	Empirical Formula	Ratio
Water	H₂O	H₂O	1:1
Hydrogen Peroxide	H₂O₂	HO	2:1
Glucose	C₆H₁₂O₆	CH₂O	6:1
Benzene	C₆H₆	CH	6:1
Ethane	C₂H₆	CH₃	2:1

Common Atomic Masses

H: 1.008 g/mol

He: 4.003 g/mol

Li: 6.941 g/mol

Be: 9.012 g/mol

B: 10.81 g/mol

C: 12.01 g/mol

N: 14.01 g/mol

O: 15.999 g/mol

F: 18.998 g/mol

Ne: 20.18 g/mol

Na: 22.99 g/mol

Mg: 24.31 g/mol

Al: 26.98 g/mol

Si: 28.09 g/mol

P: 30.97 g/mol

How to Find Empirical Formula

Enter Element Composition

Input the symbol and percent composition or mass for each element in the compound.

Convert to Moles

The calculator converts percentages to grams, then to moles using atomic masses.

Get Simplest Ratio

Mole values are divided by the smallest to find the whole-number ratio for the formula.

Why Use This Empirical Formula Calculator?

✓Step-by-Step Accuracy

Automatically handles percent-to-gram conversion, mole calculation, and ratio simplification.

✓Dynamic Element Addition

Add or remove elements to analyze compounds with any number of constituent elements.

✓Visual Composition Chart

Pie chart displays the percent composition of each element in your compound.

✓Built-in Atomic Masses

Includes atomic masses for 30+ common elements for accurate mole calculations.

✓Educational Reference

Comparison table shows empirical vs molecular formulas for common compounds.

Frequently Asked Questions About Empirical Formulas

What is the difference between empirical and molecular formula?

Empirical formula shows the simplest whole-number ratio of atoms, while molecular formula shows the actual number. For example, glucose has molecular formula C₆H₁₂O₆ but empirical formula CH₂O.

How do you calculate empirical formula from percent composition?

Convert percentages to grams (assume 100g sample), divide by atomic masses to get moles, divide all by the smallest mole value, and multiply to get whole numbers if needed.

Can empirical formula be the same as molecular formula?

Yes, for some compounds like water (H₂O), the empirical and molecular formulas are identical because the ratio cannot be simplified further.

What if the mole ratio is not a whole number?

Multiply all ratios by the same integer (2, 3, 4, etc.) until you get whole numbers. For example, a ratio of 1:1.5 becomes 2:3 when multiplied by 2.

How do you find molecular formula from empirical formula?

Divide the molecular mass by the empirical formula mass to get a multiplier, then multiply all subscripts in the empirical formula by this number.

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