Empirical Formula Calculator

A ratio, not a molecule — glucose, acetic acid and formaldehyde all reduce to CH2O.

Empirical formulaCH2Othe ratio of atoms, not the molecule

Empirical formula mass30.026 g/mol

Percentages given100%they account for the whole sample

Moles of C in 100 g3.3302840 g divided by 12.011 g/mol

Moles of H in 100 g6.656756.71 g divided by 1.008 g/mol

Moles of O in 100 g3.3308353.29 g divided by 15.999 g/mol

Empirical units per molecule6.0001a clean whole number, as it must be

Molecular formulaC6H12O6the empirical formula multiplied through

An empirical formula is a ratio. CH2O is formaldehyde at 30 g/mol, acetic acid at 60 and glucose at 180, and their percent compositions are identical. Only a separately measured molar mass separates them.

The formula

divide each percentage by its atomic weight, then reduce to the smallest whole-number ratio

Percentages to moles to a ratio

Take 100 g of the substance, so the percentages become grams directly. Divide each by its atomic weight to get moles, then divide everything by the smallest of those. What comes out is the ratio of atoms, and multiplying up to clear any halves or thirds gives the empirical formula.

The multiplier step is where it goes wrong

A ratio of 1 : 1.5 is really 2 : 3, and rounding it to 1 : 2 gives a formula that does not exist. This page tries multipliers up to twelve and reports failure rather than forcing a fit — if your data will not resolve to small integers, the honest conclusion is usually that a percentage is wrong.

Then the molar mass

The empirical formula is a ratio and nothing more. CH₂O is formaldehyde at 30 g/mol, acetic acid at 60 and glucose at 180 — the composition is identical in all three. Only a separately measured molar mass tells you which one you have.

Empirical is not molecular

Every method on these pages returns a ratio, because that is all a composition can determine. Glucose, formaldehyde and acetic acid all reduce to CH₂O, and no amount of elemental analysis will separate them. A molar mass from mass spectrometry or a freezing-point depression is what turns the ratio into a formula, and it has to come from a second, independent measurement.