Molecular Formula Calculator
Scale an empirical formula into the full molecular formula by comparing empirical-formula mass with known molar mass and checking that the multiplier stays chemically sensible.
Edited by Gail Joyce
This page is maintained as the follow-up tool to empirical-formula work. The multiplier method, mass checks, and examples are reviewed against standard general-chemistry references before major updates.
Molecular Formula Calculator
Enter the empirical formula and molecular mass to calculate the molecular formula. The calculator will determine the multiplier (n) and show the complete molecular formula.
Quick presets
How to Use
Enter the empirical formula and molecular mass, or tap a preset, to scale the simplest ratio into the full molecular formula.
Step 1
Enter the empirical formula
Use plain-text notation like `CH2O`, `CH`, or `HO`. Parentheses are supported for grouped formulas.
Step 2
Provide the molecular mass
Enter the measured or given molar mass in `g/mol`. The calculator uses it to find the integer multiplier `n`.
Step 3
Calculate or use a preset
Tap `Calculate` or start from a preset like glucose to see the empirical mass, multiplier, and scaled formula.
Step 4
Verify the multiplier
Check that `n` is close to a whole number and that the recomputed molecular mass matches the given value.
Table of Contents
Quickly navigate to different sections of this guide. Click any item below to jump to that section.
Understanding Molecular Formula
The molecular formula shows the actual number of atoms of each element in a molecule. Unlike the empirical formula, which shows only the simplest ratio, the molecular formula tells you exactly how many atoms are present. For example, glucose has the molecular formula C₆H₁₂O₆, meaning each molecule contains exactly 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.
The relationship between empirical and molecular formulas is simple: Molecular Formula = n × Empirical Formula, where n is a positive integer. To find n, divide the molecular mass by the empirical formula mass. Our Molecular Formula Calculator makes these calculations instant and accurate, whether you're solving chemistry problems or analyzing experimental data.
Key Differences: Empirical vs. Molecular Formula
Empirical Formula
Shows the simplest whole-number ratio of atoms. Examples: CH₂O (glucose, formaldehyde, acetic acid), CH₂ (ethylene), H₂O (water). Multiple compounds can share the same empirical formula.
Molecular Formula
Shows the actual number of atoms in a molecule. Examples: C₆H₁₂O₆ (glucose), C₂H₄O₂ (acetic acid), CH₂O (formaldehyde), C₂H₄ (ethylene). Each compound has a unique molecular formula.
The Multiplier (n)
n = Molecular Mass ÷ Empirical Formula Mass. This tells you how many times larger the molecule is compared to the empirical formula unit. For glucose, n = 180.16 ÷ 30.03 = 6, so C₆H₁₂O₆ = 6 × CH₂O.
Common Molecular Formulas Reference Table
| Compound | Empirical Formula | Molecular Formula | n | Molecular Mass (g/mol) |
|---|---|---|---|---|
| Water | H₂O | H₂O | 1 | 18.015 |
| Glucose | CH₂O | C₆H₁₂O₆ | 6 | 180.16 |
| Acetic Acid | CH₂O | C₂H₄O₂ | 2 | 60.05 |
| Formaldehyde | CH₂O | CH₂O | 1 | 30.03 |
| Ethylene | CH₂ | C₂H₄ | 2 | 28.05 |
| Benzene | CH | C₆H₆ | 6 | 78.11 |
| Hydrogen Peroxide | HO | H₂O₂ | 2 | 34.01 |
Common Mistakes
Most errors come from mixing up the empirical formula with the full molecular formula or from entering a molar mass that does not match the measured compound.
Entering the molecular formula first
Start with the simplest whole-number ratio. If you enter `C6H12O6` instead of `CH2O`, the multiplier step becomes meaningless.
Using the wrong molar mass
Use the molar mass of the full compound in `g/mol`, not the empirical-formula mass or a rounded classroom estimate from another species.
Ignoring a non-integer multiplier
If `n` is far from a whole number, recheck the inputs. A large mismatch usually means the empirical formula or molecular mass is wrong.
Using display subscripts in the input
Enter formulas as plain text like `CH2O` rather than formatted `CH₂O` to keep the parser working correctly.
Formulas and Equations
Calculating molecular formulas involves finding the empirical formula mass, determining the multiplier, and multiplying all subscripts. Our Molecular Formula Calculator does all the heavy lifting, but if you're curious about how it works, here's what's happening behind the scenes:
Step 1: Calculate Empirical Formula Mass
Calculate the molar mass of the empirical formula by summing the atomic masses of all atoms. For CH₂O: 12.01 + 2(1.008) + 16.00 = 30.026 g/mol.
This gives you the mass of one "unit" of the empirical formula.
Step 2: Calculate the Multiplier (n)
Divide the molecular mass by the empirical formula mass to find how many times larger the molecule is. For glucose: n = 180.16 ÷ 30.026 = 6.00.
n should be close to a whole number. If it's not, check your inputs or round to the nearest whole number.
Step 3: Multiply All Subscripts by n
Multiply each subscript in the empirical formula by n to get the molecular formula:
Molecular Formula = n × Empirical Formula
For glucose: n = 6, so CH₂O becomes C₆H₁₂O₆. Each subscript is multiplied by 6: C×6, H₂×6, O×6.
Worked Examples
Step-by-step solutions demonstrating how to calculate molecular formulas from empirical formulas and molecular masses. These examples show you how to use the Molecular Formula Calculator effectively.
Example 1: Glucose
Scenario: A compound has an empirical formula of CH₂O and a molecular mass of 180.16 g/mol. What is the molecular formula?
Solution:
Step 1: Calculate empirical formula mass
CH₂O = 12.01 + 2(1.008) + 16.00 = 30.026 g/mol
Step 2: Calculate n
n = 180.16 ÷ 30.026 = 6.00
Step 3: Multiply subscripts by n
C₁H₂O₁ × 6 = C₆H₁₂O₆
Answer: Molecular Formula = C₆H₁₂O₆
Example 2: Acetic Acid
Scenario: A compound has an empirical formula of CH₂O and a molecular mass of 60.05 g/mol. What is the molecular formula?
Solution:
Step 1: Empirical formula mass = 30.026 g/mol
Step 2: n = 60.05 ÷ 30.026 = 2.00
Step 3: CH₂O × 2 = C₂H₄O₂
Answer: Molecular Formula = C₂H₄O₂
Example 3: Benzene
Scenario: A compound has an empirical formula of CH and a molecular mass of 78.11 g/mol. What is the molecular formula?
Solution:
Step 1: Empirical formula mass = 12.01 + 1.008 = 13.018 g/mol
Step 2: n = 78.11 ÷ 13.018 = 6.00
Step 3: CH × 6 = C₆H₆
Answer: Molecular Formula = C₆H₆
Example 4: When n is Not Exactly Whole
Scenario: A compound has an empirical formula of C₂H₄O and a molecular mass of 88.10 g/mol. What is the molecular formula?
Solution:
Step 1: Empirical formula mass = 2(12.01) + 4(1.008) + 16.00 = 44.052 g/mol
Step 2: n = 88.10 ÷ 44.052 = 2.00
Step 3: C₂H₄O × 2 = C₄H₈O₂
Answer: Molecular Formula = C₄H₈O₂
Frequently Asked Questions (FAQs)
Got questions? We've got answers. Here are the most common things people ask about molecular formulas and using this Molecular Formula Calculator.
What is a molecular formula?
A molecular formula shows the actual number of atoms of each element in a molecule. For example, glucose has the molecular formula C₆H₁₂O₆, meaning each molecule contains exactly 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms.
What's the difference between empirical and molecular formula?
The empirical formula shows the simplest ratio (e.g., CH₂O), while the molecular formula shows the actual number of atoms (e.g., C₆H₁₂O₆). The molecular formula is always a multiple of the empirical formula: Molecular Formula = n × Empirical Formula.
How do I calculate molecular formula from empirical formula?
Calculate the empirical formula mass, divide the molecular mass by the empirical formula mass to get n, then multiply all subscripts in the empirical formula by n. Our Molecular Formula Calculator does this automatically!
What if n is not a whole number?
If n is close to a whole number (like 5.98 or 6.02), round to the nearest whole number. Small deviations are due to measurement uncertainty. If n is far from a whole number, check your inputs—you may have the wrong empirical formula or molecular mass.
Can multiple compounds have the same empirical formula?
Yes! Many compounds can share the same empirical formula. For example, glucose (C₆H₁₂O₆), acetic acid (C₂H₄O₂), and formaldehyde (CH₂O) all have the empirical formula CH₂O. The molecular formula distinguishes them.
How do I find molecular mass experimentally?
Molecular mass can be determined using mass spectrometry, freezing point depression, boiling point elevation, or vapor density measurements. These techniques measure the mass of molecules directly or indirectly.
What if the empirical and molecular formulas are the same?
When n = 1, the empirical and molecular formulas are identical. Examples include water (H₂O), formaldehyde (CH₂O), and carbon dioxide (CO₂). This happens when the empirical formula already represents the smallest possible molecule.
Can I use this for ionic compounds?
For ionic compounds, we typically use formula units rather than molecules. However, the concept is similar—you can determine the formula unit from empirical data and formula mass. The calculator works for both molecular and ionic compounds.
What units should I use for molecular mass?
Always use grams per mole (g/mol) for molecular mass. This is the standard unit in chemistry. The calculator expects molecular mass in g/mol.
How accurate do my measurements need to be?
For most purposes, 2-3 significant figures are sufficient. Small rounding errors won't significantly affect the molecular formula. However, very precise measurements (4+ significant figures) are needed for research applications.
What if I don't know the empirical formula?
You need the empirical formula to calculate the molecular formula. If you only have percent composition, use our Empirical Formula Calculator first to find the empirical formula, then use this calculator to find the molecular formula.
Can I calculate empirical formula from molecular formula?
Yes! Divide all subscripts in the molecular formula by their greatest common divisor (GCD). For example, C₆H₁₂O₆ → divide by 6 → CH₂O. This gives you the empirical formula.
What is the relationship between molecular mass and empirical formula mass?
Molecular Mass = n × Empirical Formula Mass, where n is a positive integer. This relationship allows you to find the molecular formula from the empirical formula and molecular mass.
How do I handle compounds with parentheses in the empirical formula?
When multiplying by n, multiply everything inside the parentheses by n. For example, if empirical formula is (NH₄)₂SO₄ and n = 1, the molecular formula is (NH₄)₂SO₄. If n = 2, it becomes (NH₄)₄S₂O₈.
What if my molecular mass is very large?
Large molecular masses are common for polymers and complex organic molecules. The calculator handles any size. Just make sure your empirical formula is correct and your molecular mass is accurate.
Can I use this for determining isomers?
Molecular formulas show composition but not structure. Isomers have the same molecular formula but different structures. For example, C₂H₆O could be ethanol (CH₃CH₂OH) or dimethyl ether (CH₃OCH₃). Additional techniques are needed to distinguish isomers.
What if I get an error message?
Error messages usually indicate invalid empirical formula format, missing molecular mass, or unknown elements. Make sure your empirical formula uses standard notation, enter a valid molecular mass, and use recognized element symbols.
How do I verify my molecular formula is correct?
Calculate the molecular mass from your molecular formula and compare it to the given molecular mass. They should match closely. You can also check if the molecular formula makes chemical sense and matches known compounds.
What is the difference between molecular mass and molar mass?
They're essentially the same thing! Molecular mass (molecular weight) refers to the mass of one molecule, while molar mass refers to the mass of one mole. Both are expressed in g/mol and have the same numerical value.
Can I use this for organic compounds?
Absolutely! The Molecular Formula Calculator works for all types of compounds, including organic compounds. Many organic compounds have the same empirical formula but different molecular formulas, making this calculator essential for identification.
What if my empirical formula has subscripts that are already large?
No problem! The calculator handles any subscript size. When you multiply by n, all subscripts are multiplied. For example, if empirical formula is C₁₀H₂₀O₁₀ and n = 2, the molecular formula is C₂₀H₄₀O₂₀.
How do I handle hydrated compounds?
For hydrated compounds like CuSO₄·5H₂O, treat the water molecules separately. First determine the molecular formula of the anhydrous compound, then add the water molecules. The calculator handles hydrated formulas if entered correctly.
What if I make a mistake entering the empirical formula?
Click the "Reset" button to clear all inputs and start over. Make sure to use standard notation (e.g., CH2O, not CH₂O) and check that all element symbols are correct.
Can I calculate molecular formula from percent composition alone?
No, you need both percent composition (to find empirical formula) and molecular mass (to find n). Use our Empirical Formula Calculator first to find the empirical formula from percent composition, then use this calculator with the molecular mass.
What is the significance of n in molecular formulas?
n tells you how many times larger the molecule is compared to the empirical formula unit. It's always a positive integer. A larger n means a larger, more complex molecule. For example, glucose (n = 6) is much larger than formaldehyde (n = 1), even though they share the same empirical formula.
References and Further Reading
For more in-depth information about molecular formulas, empirical formulas, and related topics, consult these authoritative sources:
| Resource | Description | Category |
|---|---|---|
| OpenStax Chemistry 2e | Textbook reference for empirical formulas, molecular formulas, and molar-mass scaling | Chemistry Textbook |
| ChemLibreTexts: General Chemistry | Background on formula notation, empirical formulas, and molecular-formula derivation | General Chemistry |
| PubChem | Reference molecular weights, identifiers, and compound records for verification | Chemical Data |
| NIST Chemistry WebBook | Reliable molar-mass and compound-property data for checking calculated formulas | Reference Data |
| NIST Chemistry WebBook | Standard reference data for chemical compounds | Chemical Data |
| ChemSpider | Free chemical structure database | Chemical Data |
| Royal Society of Chemistry | Professional chemistry resources and publications | Professional |