Chemistry
Molecular Weight Calculator
Parse a supported plain chemical formula, calculate molar mass, atom count, sample mass, and carbon and hydrogen mass fractions. The molecular-composition visual shows each parsed element's contribution.
Molar mass (g per mol)-
Atoms per formula unit-
Sample mass (g)-
Carbon mass fraction-
Hydrogen mass fraction-
Decision view
Parsed molecular composition
Parsed molecular compositionSupported element counts and atomic-weight contributions reconcile to total molar mass and sample mass.
Exact scenario comparisonSample amount (mol) changes while all other entered assumptions remain constant.
| Sample amount (mol) | Molar mass (g per mol) | Atoms per formula unit | Sample mass (g) | Carbon mass fraction | Hydrogen mass fraction |
|---|
How to use Molecular Weight Calculator
- Enter conventional element symbols with correct capitalization.
- Confirm the formula's hydration, salt, isotope, and charge form before use.
- Match the resulting molar mass to the substance and purity stated on the material record.
Calculator guide
Understanding Molecular Weight Calculator
Molar mass is the sum of each supported element's atomic weight multiplied by its count in the formula. Formula parsing must preserve capitalization because Co and CO describe different compositions.
Calculation method
How the calculation works
Parse a conventional element-and-count formula, sum standard atomic weights, and calculate sample mass plus carbon and hydrogen mass fractions. Tokenize element symbols and following integer counts, sum atomic-weight contributions, total atoms, multiply molar mass by sample moles, and divide carbon or hydrogen contribution by total mass.
Formula audit
Check the formula before trusting the mass
Most large errors begin with the wrong chemical form rather than arithmetic.
Worked situations
Practical examples
- C6H12O6 contains 24 atoms per formula unit.
- Using standard atomic weights, molar mass is about 180.156 g/mol.
- At 0.5 mol, sample mass is about 90.078 g; carbon contributes roughly 40.0% by mass.
Better inputs
Useful tips
- Expand unsupported parentheses or hydrates manually only when chemically correct.
- Use the exact formula of the supplied material, including waters of hydration.
- Keep more digits internally than the final reported precision.
Before relying on the result
Limitations and common mistakes
- The parser supports only the element-and-integer pattern implemented by the page.
- Parentheses, nested groups, hydrates, isotopes, charges, decimals, and unsupported elements may fail or be misread.
- Atomic weights are conventional averages and do not encode isotopic composition.
Reference
Key terms
- Molar mass
- Mass in grams of one mole of specified formula units.
- Atomic weight
- Conventional relative atomic-mass value used for an element.
- Formula unit
- Composition represented by the entered formula.
- Mass fraction
- Element mass contribution divided by total formula mass.
Important note
Calculated from the entered values using the displayed chemical relationship. Confirm identity, units, purity, conditions, and laboratory safety requirements.
Frequently asked questions
Why does capitalization matter?
Element symbols begin with a capital letter; a following lowercase letter belongs to the same symbol.
Can I enter Ca(OH)2?
Parentheses are outside this page's simple parser unless explicitly supported; expand only with care.
Is molecular weight the same as molar mass?
They are often used informally together, though relative molecular mass is dimensionless and molar mass uses g/mol.
Why can reference values differ slightly?
Atomic-weight conventions and displayed rounding can differ.