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

Empirical Formula Calculator

You can calculate an empirical formula from element masses or mass percentages by converting to moles, dividing by the smallest amount and scaling to small whole numbers.

Runs in your browserFree · No sign-up · No watermark
MASSES → FORMULARuns 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
MASSES → FORMULA
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Chemistry Tools

About Empirical Formula Calculator

An empirical formula gives the simplest whole-number ratio of elements in a compound. It is what you get from percentage composition data, and it is the step before a molecular formula when the compound's molar mass is known. It does not say how many atoms are in one molecule.

This calculator accepts element masses or mass percentages, converts each element to moles with the standard atomic weights, divides by the smallest amount and scales the ratios until they are whole numbers. Percentages that do not add up to 100% are normalized first, with a note explaining the adjustment.

What this tool does

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

  • Mass or percentage input

    Switch between measured masses in grams and mass percentages; the conversion to moles is handled for you either way.

  • Whole-number scaling

    Ratios are multiplied by the first integer from 1 to 10 that brings every value within a small tolerance of a whole number, then reduced to the simplest form.

  • Percentage normalization

    When percentages do not sum to 100%, they are normalized to a 100% total and the tool says so instead of silently distorting the result.

  • Mole-ratio table

    The table shows each element's input value, atomic mass, moles, ratio and final whole number so every step can be checked.

  • Formula formatting

    Carbon-containing formulas follow the usual carbon-then-hydrogen ordering, while formulas without carbon keep a conventional element order.

  • Clear errors

    Unknown symbols, duplicate elements, non-positive values and ratios that do not resolve are reported instead of guessed.

How to use Empirical Formula Calculator

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

    Choose the data you have

    Select mass percent if you have percentage composition, or mass if you weighed each element or were given masses.

  2. 02

    Enter the elements

    Type an element symbol and its mass or percentage in each row; use the add button for more elements and the symbol field suggests known elements.

  3. 03

    Read the mole ratio

    The table converts each value to moles, divides by the smallest amount and scales to whole numbers for the formula.

  4. 04

    Check the scaling factor

    If the ratios needed multiplying, the summary shows the factor that was applied and the reduction that followed.

  5. 05

    Use the formula

    Copy the empirical formula and, if a molar mass is known, take it to the molecular formula calculator to find the multiple.

How this tool works

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

Limitations worth knowing

  • Assumes the element masses or percentages are accurate; small analytical errors can change the last digit of the formula.
  • Percentages are assumed to describe the whole compound and are normalized when they do not total 100%.
  • Finds empirical formulas only; the molecular formula needs a molar mass and is calculated by the separate molecular formula tool.

Privacy and file handling

Element values are processed only in your browser tab. Nothing is uploaded, stored or logged, and the calculator makes no network request.

Read the full privacy policy

Empirical Formula Calculator FAQ

Short, direct answers to the questions people ask before using this tool.
How do I calculate an empirical formula from mass percentages?
Assume a 100 g sample so each percentage becomes grams, divide each mass by the element's atomic mass to get moles, divide every result by the smallest mole amount, and multiply until all ratios are whole numbers. The final integers are the formula subscripts.
What if the mole ratios are not whole numbers?
Multiply every ratio by the same small integer until they are all within tolerance of whole numbers. For example, ratios of 1 and 1.5 become 2 and 3 when multiplied by 2, giving a formula with those subscripts; this calculator searches multipliers 1 to 10.
Why does the calculator normalize percentages that do not add to 100?
If the percentages sum to 99% or 101%, the usual explanation is rounding or a small unaccounted component. Normalizing to 100% preserves the element ratios, and the tool shows a note so you know the adjustment was made rather than hidden.
What is the difference between an empirical and a molecular formula?
An empirical formula shows the simplest whole-number ratio, while a molecular formula shows the actual number of atoms in one molecule. Glucose has the empirical formula CH2O and the molecular formula C6H12O6, a multiple of six.
Does the order of the elements matter in the input?
No. The mole-ratio calculation is independent of row order. The output formula follows the usual carbon-then-hydrogen convention when carbon is present; formulas without carbon keep a conventional order such as NaCl or MgO.
Can I enter masses in grams from an actual sample?
Yes. Absolute masses work because only the ratios matter: the same sample scaled up or down gives the same formula. If you have percentages instead, switch the input mode to mass percent.
Why does the calculator reject my ratios?
The ratios may not correspond to a small whole-number formula within the multiplier range of 1 to 10, which usually means the masses or percentages are inaccurate. Check the data and, if it came from analysis, its precision before overriding by hand.

Background reading

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