Molecular Formula Calculator

The Molecular Formula Calculator finds the true chemical formula of a compound from its simplest repeating unit — useful in chemistry when you know the basic atomic ratio but need the actual formula for a molecule. Enter your Empirical Formula (e.g. CH₂O) and Molecular Mass in g/mol to get the full Molecular Formula, along with the Empirical Formula Mass, the Multiplier (n) showing how many times the empirical unit repeats, and the Percent Composition of each element.

Enter the simplest whole number ratio formula

g/mol

Molecular weight in grams per mole

Results

Molecular Formula

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Empirical Formula Mass

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Multiplier (n)

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Percent Composition

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Results Table

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Frequently Asked Questions

What is the difference between empirical and molecular formula?

The empirical formula shows the simplest whole number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms of each element in a molecule. For example, glucose has empirical formula CH2O but molecular formula C6H12O6.

How do you calculate molecular formula from empirical formula?

First, calculate the empirical formula mass. Then divide the molecular mass by the empirical formula mass to get the multiplier (n). Finally, multiply each subscript in the empirical formula by this multiplier to get the molecular formula.

What information do I need to find the molecular formula?

You need two pieces of information: the empirical formula (simplest ratio) and the molecular mass (molar mass) of the compound. With these, you can determine the exact molecular formula.

Can the empirical and molecular formulas be the same?

Yes, when the molecular formula is already in its simplest form, it will be the same as the empirical formula. Examples include water (H2O), carbon dioxide (CO2), and methane (CH4).

How accurate should the molecular mass be?

For most calculations, molecular mass accurate to 2-3 decimal places is sufficient. However, more precise values will give more accurate results, especially when dealing with large molecules or precise analytical work.

What if my calculated multiplier is not a whole number?

If the multiplier is very close to a whole number (within 0.1), round to the nearest integer. If it's significantly different, check your empirical formula and molecular mass values for accuracy, as experimental error might be affecting your results.