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Chemistry Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Molecular Formula Calculator

You can find a molecular formula from an empirical formula and a molar mass, or start from mass percentages, by dividing the molar mass by the empirical formula mass.

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EMPIRICAL → MOLECULARRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
EMPIRICAL → MOLECULAR
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Molecular Formula Calculator

A molecular formula tells you how many atoms of each element are in one molecule, while an empirical formula gives only the simplest ratio. The molecular formula is the empirical formula multiplied by a whole number n, which follows from the compound's molar mass.

This calculator takes an empirical formula and a molar mass, computes n = molar mass / empirical formula mass, and rejects results that are not close to a whole number instead of rounding blindly. Mass percentages can also be used as the starting point, with the empirical formula calculated first.

What this tool does

The details that matter when you use Molecular Formula Calculator for real work.

  • Two starting points

    Start from an empirical formula such as CH2O, or enter mass percentages and let the tool find the empirical formula first.

  • Whole-number multiplier

    The calculator divides the molar mass by the empirical formula mass and reports n with the rounding tolerance that was applied.

  • Multiplied formula

    Every subscript in the empirical formula is multiplied by n, and the resulting atom counts are shown in a comparison table.

  • Honest rejection

    When n is not within 0.15 of an integer, the result is rejected with the computed ratio so a wrong molar mass is not silently rounded into a formula.

  • Composition route

    Mass percentages are converted to an empirical formula using the same helper as the empirical formula calculator, including normalization notes.

  • Worked steps

    Both the empirical formula mass and the n conversion are written out, so the molecular mass can be checked against the given molar mass.

How to use Molecular Formula Calculator

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose the starting point

    Pick empirical formula if you already have one, or mass percent if you are starting from composition data.

  2. 02

    Enter the molar mass

    Type the compound's molar mass in g/mol; it is the measured or given value that determines the multiplier.

  3. 03

    Add the formula or percentages

    Type the empirical formula, or enter at least two element percentages with their symbols in the rows.

  4. 04

    Read n and the formula

    The result shows n, the empirical formula mass and the molecular formula with each subscript multiplied.

  5. 05

    Check the working

    The step panel shows the empirical formula, its mass, the division and the multiplication into the molecular formula.

How this tool works

Works with
EMPIRICAL → MOLECULAR
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Assumes the given molar mass belongs to the same compound and is accurate enough for n to land within tolerance of an integer.
  • A molecular formula is meaningful for molecular compounds; for ionic solids the empirical formula is usually the more appropriate description.
  • Does not use isotope-specific masses or account for mixtures, so measured molar masses of mixtures may not resolve to a clean multiple.

Privacy and file handling

Formulas, percentages and molar masses are processed in your browser tab. Nothing is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Molecular Formula Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
How do I find the molecular formula from an empirical formula?
Divide the compound's molar mass by the empirical formula mass to get n, round n to the nearest whole number if it is within tolerance, then multiply every subscript in the empirical formula by n. For CH2O with a molar mass of 180.16 g/mol, n is 6 and the molecular formula is C6H12O6.
What if n is not a whole number?
A non-integer n usually means the molar mass or the empirical formula is wrong, or that the data describe a mixture. This calculator only accepts n within 0.15 of an integer and otherwise reports the computed ratio so the input can be checked instead of rounded.
What is the difference between empirical and molecular formula?
The empirical formula is the simplest whole-number ratio of atoms, while the molecular formula gives the actual atom count per molecule. The molecular formula is always a whole-number multiple of the empirical formula, and that multiple comes from the molar mass.
Can I start from mass percentages instead of a formula?
Yes. Switch to mass percentage mode and enter each element with its percentage. The tool converts the percentages to an empirical formula first, then applies the same n = molar mass / empirical mass step, and shows both stages in the working.
How accurate does the molar mass need to be?
Accurate enough that n lands close to a whole number; this calculator allows a tolerance of 0.15 in n. A rough molar mass from a melting point or a mass spectrum is often sufficient, but a wrong value can push n outside tolerance and trigger a rejection.
Does this tool work for hydrates and ionic compounds?
The formula parser accepts hydrates and brackets, but molecular formulas are most meaningful for molecular compounds. For ionic solids, the empirical formula is the formula unit, and the multiple n may not have a simple molecular interpretation.
Why is the molecular formula a multiple of the empirical formula?
Both formulas describe the same compound, so they contain the same element ratio. The empirical formula is the ratio reduced to the smallest integers, and the molecular formula restores the actual count by multiplying that ratio by the number of formula units in one molecule.

Background reading

Format guides that explain the trade-offs behind Molecular Formula Calculator.