Formula & Molecular Mass

Empirical Formula Calculator

Find the smallest whole-number formula from element masses or percentages.

1

Enter values

Enter element:value pairs. Use commas, semicolons, or new lines. Example: C:40%, H:6.7%, O:53.3%.
Advanced options
Examples
2

Results

Ready to calculate

Your result, units, method, and version information will appear here.

How to use this calculator

  1. Enter each element symbol and its mass or percentage.
  2. Separate the element-value pairs with commas.
  3. Calculate and check the normalized mole ratios.
  4. Change the tolerance only when measurement uncertainty supports the change.

Formula and variables

ratioᵢ = (massᵢ/Aᵢ) / min(mass/A)

SymbolMeaningUnit
massᵢelement massg or %
Aᵢatomic massg/mol
ratioᵢwhole-number ratiodimensionless

Worked example

C:40.0, H:6.7, O:53.3 by mass produces a mole ratio close to CH2O.

Interpretation

The accepted multiplier is the smallest one that moves every normalized ratio within the visible tolerance of an integer.

Common mistakes

  • Use a consistent mass basis for all values.
  • Do not hide noisy ratios with an excessively broad tolerance.

Frequently asked questions

Can I enter percentages instead of masses?

Yes. Treat each percentage as grams in a 100 g sample.

Do the percentages have to total exactly 100?

No. Small differences can result from rounding or measurement uncertainty.

Why does the calculator use a ratio multiplier?

A multiplier converts ratios such as 1.5 or 1.33 to defensible whole-number subscripts.

Can I use scientific notation?

Yes. Enter values such as 6.022e23 or 1.0e-6 in a numeric field.

How should I round the result?

Keep extra digits during the calculation. Round the final result to the precision required by your data.

Sources