Worked example: Molecular Weight Calculator
Water. This fixed reference example shows one complete scenario; the interactive results above use your current inputs.
View the example inputs
- Chemical formula
- H2O
| Calculated quantity | Example result |
|---|---|
| Molar mass | 18.015 g/mol |
Keeping chemical amounts and units consistent
Distinguish mass, amount and concentration
Mass in grams, amount in moles and concentration in moles per liter are related but different quantities. Converting mass to moles needs a molar mass, and calculating molarity needs the final solution volume rather than the volume of solvent before dissolving.
A formula-based molar mass sums the specified element counts using the stated atomic-mass table. Parentheses multiply a group, and a hydrate coefficient applies to the component after the dot. Average atomic masses do not identify a particular isotope.
Check the physical quantity being calculated
Density is mass per volume. Weight is a force that also depends on gravitational acceleration. Converting one of these quantities without the needed physical assumption can produce a plausible number with the wrong meaning.
Use the units shown by the form and review supported chemical notation. A mathematical concentration or amount does not establish purity, suitability, reaction yield or a laboratory procedure.
Formula and calculation method
Sums atom counts using the NIH PubChem periodic table, retrieved October 2026. Example: CuSO4·5H2O. Uses average atomic masses; radioactive elements may use representative mass numbers.
Supports all 118 elements. Does not parse charges, isotope labels, chemical equations or ambiguous plain-dot hydrate syntax.
Reference Sources
Frequently asked questions
How does this calculator work?
Sums atom counts using the NIH PubChem periodic table, retrieved October 2026. Example: CuSO4·5H2O. Uses average atomic masses; radioactive elements may use representative mass numbers.
What assumptions should I check?
Supports all 118 elements. Does not parse charges, isotope labels, chemical equations or ambiguous plain-dot hydrate syntax.
Can I save or print this calculation?
Use Copy link with inputs to reproduce the scenario, Download results for a text record, or Print. Where a schedule is shown, its CSV download includes every row.