Molecular Formula Calculator

Scaling an Empirical Formula Up to the Real Thing

An empirical formula only captures a ratio — it says nothing about the compound's actual size. Glucose and formaldehyde share the exact same empirical formula, CH2O, yet one is a simple gas and the other a six-carbon sugar. The missing piece is the compound's true molar mass, which reveals how many times larger the molecular formula is than its empirical ratio.

The Formula

Multiplier = round(Molar Mass ÷ Empirical Formula Mass)
Molecular Formula = Empirical Formula subscripts × Multiplier

The empirical formula mass is computed from the entered element counts, and the multiplier tells you how many empirical units make up one full molecule.

Where This Calculation Matters

Identifying an unknown compound — combined with a mass spectrometry or freezing-point-depression molar mass measurement, this pins down the true molecular formula.
Distinguishing compounds sharing an empirical formula — acetylene (C2H2) and benzene (C6H6) share the empirical formula CH, but are very different molecules.
Confirming a synthesized product — comparing an expected molecular formula's mass against a measured molar mass validates a synthesis.
Polymer and oligomer characterization — determining how many repeat units make up an observed molecular weight.

A Worked Example: From CH2O to Glucose

The empirical formula CH2O has a formula mass of 30.026 g/mol (12.011 + 2 × 1.008 + 15.999). If the compound's actual molar mass is measured at 180.156 g/mol:

Multiplier = round(180.156 ÷ 30.026) = 6
Molecular Formula = C(1×6)H(2×6)O(1×6) = C6H12O6

That's glucose — six times larger than its empirical formula, exactly as the multiplier predicts.

How to Use This Calculator

Enter each element of the empirical formula in Element 1 Symbol through Element 4 Symbol, with its subscript in the matching count field.
Enter the compound's Actual Molar Mass as measured or given.
Select Calculate to get the scaled-up molecular formula.

Related Calculations

Don't have the empirical formula yet? Derive it first with the Empirical Formula Calculator. To verify the resulting molecular formula's mass, cross-check it with the Molar Mass Calculator.