Molecular Weight Calculator
Calculate molar mass and elemental composition from any chemical formula
• Numbers follow elements: H2O, not H₂O
• Parentheses supported: Ca(OH)2, Al2(SO4)3
• Case-sensitive: Na ≠ na
Real-Life Guide to Using the Molecular Weight
Molecular mass from formula. Use the examples and checks below to turn the number into a practical decision.
When this calculator is useful
Needed whenever you have a chemical formula and must find its molar mass — for stoichiometry calculations, preparing molar solutions, or verifying reagent purity by weight.
For most people, the best way to use the Molecular Weight is to try the real case first, then change one input at a time. That makes the trade-off visible. For example, with a loan calculator you can change tenure while keeping the same rate; with an investment calculator you can change return assumption while keeping the same monthly contribution; with a health, education or measurement calculator you can check how much one input changes the final category.
The result should answer a practical question: Can I afford this? How much should I save? Is this score enough? Is this measurement within range? What is the safer or cheaper option? If the output does not answer the decision clearly, adjust the inputs until the scenario matches your real situation.
Practical Advice
Use the Molecular Weight as a planning tool, not just a number generator. Write down the inputs you used, because the final answer is meaningful only when you remember the assumptions behind it.
If the decision affects money, health, tax, safety, academics or legal compliance, keep a second check ready. That second check may be a bank quote, payslip, official rule, prescription, site measurement, mark sheet or invoice.
Common Mistakes
- Miscounting atoms inside parentheses — Ca(OH)₂ contains 2 oxygen and 2 hydrogen atoms, not 1 of each, because the subscript outside the bracket multiplies everything inside it.
- Confusing an element's atomic number with its atomic mass — using 6 for carbon (its atomic number) instead of 12.01 g/mol (its atomic mass).
- Forgetting to include water of hydration in a formula, such as leaving out the extra 5 × 18.02 = 90.10 g/mol contributed by the water in CuSO₄·5H₂O.
- Rounding each atomic mass too aggressively before summing, which compounds into a noticeably wrong total for molecules with many atoms.
- Treating molecular weight and formula weight as always identical — for ionic compounds without discrete molecules (like NaCl), the term 'formula weight' is technically more correct, though the number is calculated the same way.
How to Interpret Results
The output is the molar mass in grams per mole (g/mol) — use it directly to convert between a measured mass and the number of moles it represents, which is the basis for every stoichiometric calculation that follows.
A good interpretation looks at both the main result and the supporting values. If a page shows totals, ratios, categories, schedules or warnings, read those together instead of focusing only on the biggest number.
Molecular Weight FAQs
Useful answers for interpreting the output, avoiding mistakes and using the result responsibly.
About Molecular Weight
Molecular weight (molar mass) is the sum of atomic weights of all atoms in a formula, in grams per mole (g/mol). One mole of any substance contains 6.022 × 10²³ particles (Avogadro's number). Molar mass is essential for stoichiometry calculations — converting between grams and moles.
Common molar masses: H₂O = 18.015, NaCl = 58.44, CO₂ = 44.01, glucose (C₆H₁₂O₆) = 180.16, ethanol (C₂H₅OH) = 46.07 g/mol. Atomic weights used are 2021 IUPAC standard values.