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Composition · Chemical formulas

Empirical & Molecular Formula Calculator

Derive an empirical formula from elemental masses or percentages, then use measured molar mass to test the corresponding molecular formula.

Formula shown Runs locally Reviewed Aug 11, 2026
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Equation guide

Elemental mass composition converted to relative amounts of substance

Element moles

ni = mi/Mi

Normalized ratio

ri = ni/nmin

Molecular multiplier

n = Mmolecular/Mempirical
Composition analysis

Derive the simplest and molecular formulas

ElementMass percent

Use elemental mass percentages or masses from one sample. Inputs and displayed values use at most three decimal places. The tool searches multipliers up to 12 for a defensible small whole-number ratio.

mass → moles → ratio

Enter an elemental composition to obtain the empirical formula.

Using the model

Symbols, assumptions and limitations

Interpretation notes

Elemental amounts are converted to moles and divided by the smallest amount before a small whole-number ratio is selected. Percentage data should total 100%. A molecular formula requires a measured molar mass close to an integer multiple of the empirical-formula mass.

Worked examples

See the method in practice

01

Glucose

A 40.000% C, 6.714% H, and 53.286% O composition gives the empirical formula CH₂O. Its molar mass supports a multiplier of six and molecular formula C₆H₁₂O₆.

02

Hydrogen peroxide

The elemental composition reduces to empirical formula HO, while a molar mass near 34.014 g/mol gives H₂O₂.

Questions

Frequently asked

Why divide by the smallest mole amount?

This normalizes all elemental amounts to a relative ratio while preserving their proportions.

Why might the ratios not be close to integers?

Subscripts such as 1.5 or 1.333 require multiplying all ratios by 2 or 3. Poor analytical data or a missing element can also prevent a reliable ratio.

Can the molecular formula equal the empirical formula?

Yes. That occurs when the measured molar mass is approximately the empirical-formula mass, so the multiplier is one.

Sources & review

Equations and examples are checked against the references below. Results are educational and should be independently verified for safety-critical work.

OpenStax Chemistry — Determining Empirical and Molecular Formulas

Written by the STEM Hub editorial team · Reviewed August 11, 2026 · Review methodology