Empirical Formula Calculator

Formula meaning

What is an empirical formula?

An empirical formula describes the simplest whole-number ratio of the elements in a compound. For example, glucose has the molecular formula C₆H₁₂O₆, but its empirical formula is CH₂O because the subscripts can all be divided by six.

The empirical formula does not always represent the actual number of atoms in a molecule. It expresses the lowest ratio supported by composition data.

Calculation method

How to calculate an empirical formula

Convert each element amount to moles by dividing it by the element atomic mass:

Next, divide every mole value by the smallest mole value:

If the ratios are not sufficiently close to whole numbers, multiply every ratio by the same small integer. The resulting whole numbers become the formula subscripts.

Calculator instructions

How to use the empirical formula calculator

1. Select percentage composition or mass as the input basis.
2. Choose each chemical element in the compound.
3. Enter the percentage or measured mass for every element.
4. Add more element rows when the compound contains additional elements.
5. Calculate and review the mole values, normalized ratios, and final subscripts.

Percentage composition example

Finding CH₂O from percentage composition

Consider a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. Treating the percentages as masses in a 100-gram sample gives the following approximate mole amounts:

1. Carbon: 40.0 ÷ 12.011 = 3.330 mol
2. Hydrogen: 6.7 ÷ 1.008 = 6.647 mol
3. Oxygen: 53.3 ÷ 15.999 = 3.331 mol
4. Divide all values by approximately 3.330 to obtain the ratio 1:2:1.

The simplest whole-number ratio is therefore C₁H₂O₁, written as CH₂O.

Fractional ratios

Converting decimal ratios to whole numbers

Experimental and rounded composition values do not always produce exact integers. Ratios near common fractions should be multiplied together by a suitable small number.

• A ratio ending near 0.5 usually requires multiplying every ratio by 2.
• A ratio ending near 0.33 or 0.67 usually requires multiplying by 3.
• A ratio ending near 0.25 or 0.75 usually requires multiplying by 4.
• All ratios must be multiplied by the same number to preserve their relationship.

Formula comparison

Empirical formula vs. molecular formula

A molecular formula is a whole-number multiple of its empirical formula. If the empirical formula mass and the compound molar mass are known, the multiplier can be calculated:

For example, the empirical formula CH₂O has a formula mass of approximately 30.026 g/mol. Glucose has a molar mass near 180.156 g/mol. The multiplier is 6, producing C₆H₁₂O₆.

Common mistakes

Empirical-formula calculation mistakes

• Dividing element amounts by atomic numbers instead of atomic masses.
• Rounding mole values before calculating the normalized ratios.
• Rounding a value such as 1.5 directly to 2 instead of multiplying all ratios by 2.
• Using inconsistent mass units for different elements.
• Omitting an element from the complete percentage composition.
• Confusing the empirical formula with the molecular formula.

Related chemistry tools

Continue your formula calculations

Use the Molecular Weight Calculator to calculate the molar mass of an empirical or molecular formula.

Use the Mass to Moles Calculator for direct conversions between a substance mass and its amount in moles.

Use the Stoichiometry Calculator to apply balanced-equation mole ratios to reactants and products.

Use the Limiting Reactant Calculator to identify the limiting reagent and calculate theoretical product yield.

Questions and answers

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