What is the difference between empirical and molecular formula?

The empirical formula gives the simplest whole-number ratio of atoms in a compound (e.g. CH2O for glucose). The molecular formula gives the actual number of atoms in one molecule (e.g. C6H12O6 for glucose). The molecular formula is always a whole-number multiple of the empirical formula.

What format should I use for the empirical formula?

Use standard chemical notation: capitalize the first letter of each element symbol, optionally followed by a subscript count. Examples: H2O, CH2O, C2H5O, Na2SO4. Do not use dots, dashes, or parentheses.

How accurate is the molar mass lookup?

The tool uses standard atomic weights from IUPAC (2021 table) rounded to four decimal places, which is sufficient for typical analytical chemistry calculations.

What happens if n is not a whole number?

The tool rounds n to the nearest integer and flags the deviation so you can check your molar mass value. A large deviation (>5%) usually means the input molar mass is inaccurate or the empirical formula is wrong.

Can I use multi-letter element symbols like Na or Cl?

Yes. The parser handles one- and two-letter IUPAC element symbols (e.g. Cl, Br, Na, Fe). Just make sure the first letter is uppercase and the second is lowercase.

Molecular Formula Calculator

Name: Molecular Formula Calculator
Availability: InStock
Author: Nham Vu

Enter an empirical formula and molar mass to instantly calculate the true molecular formula of a compound.

Input

Empirical Formula

Uppercase first letter, lowercase second letter (Na, Cl). Counts follow the symbol.

Molar Mass (g/mol)

Quick Examples

Result

Enter an empirical formula and molar mass, then click Calculate.

Molecular Formula

Breakdown

Property	Value

Atom Counts

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Summary

Enter an empirical formula and molar mass to instantly calculate the true molecular formula of a compound.

How it works

Enter the empirical formula (e.g. CH2O) using standard chemical notation.
Enter the known molar mass of the compound in g/mol.
The tool parses each element and its count from the empirical formula.
It looks up the atomic mass of each element and computes the empirical formula mass.
The multiplier n is calculated as molar mass divided by empirical formula mass, rounded to the nearest integer.
Each element count is multiplied by n to produce the molecular formula.

Use cases

Determine the molecular formula from mass spectrometry data.
Verify combustion analysis results in an organic chemistry lab.
Check molecular formula assignments in homework or exam prep.
Convert percent-composition data (after finding empirical formula) to molecular formula.
Quickly scale empirical ratios when given a molecular weight from a literature source.
Validate results from elemental analysis reports in pharmaceutical research.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu