Enter the empirical formula and an independently determined molecular molar mass. The calculator finds the empirical formula mass, checks for a whole-number multiple and multiplies every elemental subscript.

Formula: multiplier = measured molecular molar mass ÷ calculated empirical formula mass; a molecular formula requires that ratio to be an integer; multiply every empirical element count by that integer

Worked example

CH₂O has an empirical formula mass of about 30.026 g/mol with the site’s atomic-weight table. A measured 180.156 g/mol is six times that mass, so the molecular formula is C₆H₁₂O₆.

An independent mass is essential

The empirical formula alone gives a ratio of atoms, not a unique molecule. OpenStax uses the independently known molecular mass divided by empirical formula mass to find the integer multiple.

Check whether the ratio is credible

The tool accepts a ratio within 2% of a positive whole number and reports its mismatch; a larger difference triggers an error rather than silently inventing a formula. Verify measurements, composition and rounding if no integer fits.

Formula notation and scope

Element symbols are case-sensitive. The result expands grouped formulas into elemental counts and does not infer structure or distinguish isomers. This is for discrete molecular compounds; an ionic formula unit should not be described as a molecule.

Explore the related calculation

For a different starting point, try the empirical formula calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

Found a problem? Email contact@gramstomoles.org.

Molecular formula from empirical formula calculator

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