Empirical Formula Calculator

Calculate the empirical formula from percent composition or element masses. Determine the molecular formula from empirical formula and molecular weight.

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Empirical Formula MW (g/mol)
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C subscript —
H subscript —
O subscript —
N subscript —
Empirical Formula —
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Empirical Formula
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Empirical MW (g/mol) —
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g/mol
Empirical Formula
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Mass of C (g) —
Mass of H (g) —
Mass of O (g, by diff) —
Empirical MW (g/mol) —
Molecular Formula —
Multiplier n —

How to Use This Calculator

  1. Enter the percent composition for each element (C, H, O, N). Percentages should sum to ~100%.
  2. The calculator converts to moles, finds the smallest whole-number ratio, and returns the empirical formula subscripts.
  3. Use the Empirical to Molecular tab to find the molecular formula.

Formula

moles_X = %X / MM_X

ratio_X = moles_X / min(all moles)

n = MW_molecular / MW_empirical

Example

Example: C: 40%, H: 6.67%, O: 53.33%. Moles: C=3.33, H=6.67, O=3.33. Divide by 3.33 → C:1, H:2, O:1. Empirical formula: CH₂O.

Frequently Asked Questions

  • The empirical formula gives the simplest whole-number ratio of atoms in a compound. For example, glucose C₆H₁₂O₆ has the empirical formula CH₂O (ratio 1:2:1).
  • Assume 100 g of compound. Convert each % to grams, divide by molar mass to get moles, then divide all mole values by the smallest to get ratios. Multiply to get whole numbers if needed.
  • Divide the molecular weight by the empirical formula weight to get the multiplier n. Multiply each subscript in the empirical formula by n.
  • Combustion analysis burns a compound in excess O₂ and measures the CO₂ and H₂O produced. Mass of C = mass of CO₂ × (12/44). Mass of H = mass of H₂O × (2/18). Mass of O = sample mass − C − H.
  • Compounds with the same molecular formula but different structural arrangements. For example, butane and isobutane both have formula C₄H₁₀. The empirical formula (C₂H₅) cannot distinguish them — additional data (spectroscopy) is needed.

Related Calculators

⚗️ Molar Mass Calculator ⚗️ Stoichiometry Calculator 📊 Percent Yield Calculator ⚗️ Molarity Calculator
Sources & References (5) ▾
  1. Empirical and Molecular Formulas — ACS Education — American Chemical Society
  2. OpenStax Chemistry 2e, Chapter 3 — Empirical and Molecular Formulas — OpenStax
  3. IUPAC — Nomenclature of Inorganic Chemistry (Red Book) — IUPAC
  4. NIST Chemistry WebBook — Compound Data — NIST
  5. LibreTexts Chemistry — Empirical Formula Determination — LibreTexts