Empirical Formula Calculator

Convert percent composition or masses into empirical and molecular formulas with a transparent mole-ratio table.

Composition mode

Percent Mass

Element	Amount	Actions

Mass unit

Percent mode treats entries as grams in a 100 g sample.

Molecular molar mass

Optional, used to compute the molecular formula.

Percent tolerance

Ratio tolerance

Empirical formula

Enter composition

Molecular formula

Optional

Calculation table
Element	g	Atomic mass	Moles	Ratio	Multiplied	Subscript

Export

grams / atomic mass = moles; divide by the smallest mole value How?

How this is calculated

Percent mode assumes a 100 g sample, so each percentage point is treated as one gram. Mass mode converts the entered mass to grams. Each element mass is divided by its bundled atomic mass, then every mole amount is divided by the smallest mole amount.

Ratios are multiplied by integers from 1 through 8 until all entries are within the selected tolerance of whole numbers. If a molecular molar mass is supplied, it must be close to an integer multiple of the empirical formula mass.

Formula: grams / atomic mass = moles; divide by the smallest mole value

See Sources below

Sources

OpenStax Chemistry 2e, Determining Empirical and Molecular Formulas. OpenStax. Retrieved Jul 8, 2026.
OpenStax Chemistry 2e, Formula Mass and the Mole Concept. OpenStax. Retrieved Jul 8, 2026.
NIST Atomic Weights and Isotopic Compositions. NIST. Retrieved Jul 8, 2026.

Method last reviewed July 8, 2026

How we choose and check our formulas