Empirical Formula Calculator

Find an empirical formula from mass percentages, the molecular formula from molar mass, or % composition from a formula.

I have	Mass percentages → formula
Element and mass % (or grams), one per line	C 40.0 H 6.71 O 53.29
Molar mass (optional, for the molecular formula)	180.16 g/mol

I have

Element and mass % (or grams), one per line

Molar mass (optional, for the molecular formula)

g/mol

Empirical formula

CH₂O

Empirical formula mass 30.026 g/mol. With a molar mass of 180.16 g/mol, the molecular formula is C₆H₁₂O₆ (× 6).

Working

Element	Mass	÷ atomic weight = mol	÷ smallest	Whole number
C	40	3.33028	1	1
H	6.71	6.65675	1.9989	2
O	53.29	3.33083	1.0002	1

About the Empirical Formula Calculator

The empirical formula is the simplest whole-number ratio of atoms. Divide each element's mass (or mass %, as grams in 100 g) by its atomic weight to get moles, divide by the smallest, then multiply by a small whole number if needed (ratios like 1.5 or 1.33 mean ×2 or ×3). The molecular formula is a whole-number multiple of it, found from the molar mass. Atomic weights are IUPAC standard values.

The formula

molᵢ = massᵢ ÷ Aᵢ; ratio = molᵢ ÷ min(mol); molecular = empirical × (M ÷ M_empirical)

Worked example

Glucose: C 40.0%, H 6.71%, O 53.29%

mol: 3.330, 6.657, 3.331 → ratio 1 : 2 : 1 → CH₂O (30.03 g/mol)
Molar mass 180.16 ÷ 30.03 = 6 → C₆H₁₂O₆

Questions people ask

Can I enter grams?

Yes; grams work the same as percentages.

Is the empirical formula the same as the molecular formula?

Not always. The empirical formula is the simplest whole-number ratio (CH₂O for glucose); the molecular formula is a whole-number multiple of it (C₆H₁₂O₆). The molar mass tells you the multiple.