Stoichiometry & gases · SL/HL
Empirical & Molecular Formula Calculator
Enter one element per line as: symbol amount atomic-mass. Amounts may be masses or percentages as long as they share the same basis.
Your values
Start with the example or enter your own values. Use a dot for decimals and e for scientific notation.
Calculated locally. No account or input upload.
Result & working
ExampleThe calculator is loading. The worked example is also shown below.
Step-by-step working
The formula
n(element) ∝ amount / atomic mass
ratio = n(element) / smallest n
molecular multiplier ≈ molecular molar mass / empirical-formula mass
| Symbol | Meaning |
|---|---|
| amount | Mass or percentage assigned to each element. |
| atomic mass | Relative atomic mass used to obtain mole ratios. |
When to use this calculator
The integer ratio step requires chemical judgement. The calculator searches small multipliers for a defensible whole-number ratio and reports the residual.
Worked example
The page opens with these example values. The result below is pre-generated for reference.
- C: amount/Ar = 40 / 12.011 = 3.330281
- H: amount/Ar = 6.71 / 1.008 = 6.656746
- O: amount/Ar = 53.29 / 15.999 = 3.330833
- C: 3.330281 / 3.330281 = 1
- H: 6.656746 / 3.330281 = 1.998854
- O: 3.330833 / 3.330281 = 1.000166
- Multiply ratios by 1 → 1 : 2 : 1 → CH2O.
- Molecular multiplier ≈ 180.16 / 30.026 = 6.000133 ≈ 6; molecular formula C6H12O6.
Empirical formula: CH2O
Common mistakes
- Do not round 1.50 to 2 before testing a common multiplier of 2.
- Percent composition can be treated as grams in an arbitrary 100 g sample.