Empirical Formula Calculator
ScienceFreeNo sign-up
The empirical formula is the simplest whole-number ratio of atoms in a compound. A compound that is 40.0% carbon, 6.71% hydrogen and 53.29% oxygen has the empirical formula CH2O. Add a molar mass of 180.16 g/mol and you get the molecular formula C6H12O6 (glucose).
Leave 0 to skip the molecular formula.
| Mole ratio | |
| C | 3.3303 mol → 1 → 1 |
| H | 6.6567 mol → 1.999 → 2 |
| O | 3.3308 mol → 1 → 1 |
| Formula | |
| Empirical formula | CH₂O |
| Empirical formula mass | 30.026 g/mol |
| Molecular formula | C₆H₁₂O₆ |
Show steps
- C: 40 ÷ 12.011 = 3.3303 mol; ÷ 3.3303 = 1.
- H: 6.71 ÷ 1.008 = 6.6567 mol; ÷ 3.3303 = 1.999.
- O: 53.29 ÷ 15.999 = 3.3308 mol; ÷ 3.3303 = 1.
- Empirical formula: CH₂O (mass 30.026 g/mol).
- Molecular formula: 180.16 ÷ 30.026 = 6 ≈ 6, so multiply every subscript by 6: C₆H₁₂O₆.
How to use the calculator
- Type each element symbol, such as C, H, O or Cl, with its percent by mass or its mass in grams.
- Optional: enter the molar mass of the compound to also get the molecular formula.
- Press Calculate. Show steps lists the moles and ratios for each element.
Percentages work like grams: assume a 100 g sample, so 40.0% carbon means 40.0 g of carbon.
Steps to find an empirical formula
- Change each percent to grams (assume 100 g).
- Divide each mass by the element’s molar mass to get moles.
- Divide every mole value by the smallest one.
- If a ratio ends in about .5, .33 or .25, multiply all ratios by 2, 3 or 4 to make whole numbers.
- Use the whole numbers as subscripts.
Empirical vs molecular formula
| Compound | Molecular formula | Empirical formula |
|---|---|---|
| Glucose | C6H12O6 | CH2O |
| Hydrogen peroxide | H2O2 | HO |
| Benzene | C6H6 | CH |
| Water | H2O | H2O |
To go from empirical to molecular, divide the molar mass by the empirical formula mass and multiply every subscript by that whole number.
A ratio that needs a multiplier
Iron oxide that is 69.94% Fe and 30.06% O: Fe 69.94 ÷ 55.845 = 1.252 mol, O 30.06 ÷ 15.999 = 1.879 mol. Dividing by 1.252 gives Fe 1 : O 1.50. Multiply by 2 to get Fe2O3.
Empirical formula practice questions
Test yourself with 6 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.
Quiz complete
Frequently asked questions
How do you find the empirical formula from percentages?
Treat the percents as grams in a 100 g sample, change each to moles, divide by the smallest number of moles, and round to whole numbers (multiplying first if a ratio ends in .5, .33 or .25).
What is the difference between an empirical and a molecular formula?
The empirical formula is the simplest ratio of atoms. The molecular formula is the actual number of each atom in a molecule, which is a whole-number multiple of the empirical formula.
How do you get the molecular formula?
Divide the compound's molar mass by the empirical formula mass. Multiply each subscript in the empirical formula by that whole number.
What if my ratios are not close to whole numbers?
Ratios like 1.5, 1.33 or 1.25 mean you should multiply all of them by 2, 3 or 4. Ratios such as 1.1 or 1.9 usually come from rounding the molar masses or percentages too early.
Sources
Related calculators
More science calculators
Related to This Article
More math articles
- The Best Grade 5 Math Book for Virginia Students
- 6th Grade SBAC Math FREE Sample Practice Questions
- Mississippi MAAP Algebra 1 Free Worksheets: 64 Free Skill-by-Skill Algebra 1 PDFs with Answer Keys
- Why Interactive Challenges Improve Math Skills More Than Memorization
- GED Math Practice Test Questions
- Your Math Buddy: How to Unravel the Mystery of Mutually Exclusive and Overlapping Probabilities
- What Kind of Math Is on the ACT Test?
- 4th Grade PSSA Math Practice Test Questions
- Baby Formula Calculator
- AP Cybersecurity Evidence-Based Responses: Write a Clear Recommendation (2027 Prep)
What people say about "Empirical Formula Calculator: From Percent or Grams"?
No one replied yet.