How to use the molecular weight calculator
Prepare the values for this calculation
Calculate relative molecular/formula mass from a chemical formula using NIST periodic-table atomic weights where available. Use the formula below to check that it answers your question. Read the input units before transferring figures from a statement, measurement or dataset.
Enter and check each input
- Chemical formula: use the same separators and value order as the example in the input table. Replace the example data with your own complete dataset.
The input table gives a complete example. Keep units and time periods consistent across related fields.
Calculate and resolve any input error
Choose Calculate after entering the values. Changes also update the answer after a short pause. If an error appears, follow its message, correct the field and calculate again. Reset restores the example values.
Interpret the answer
Check Relative molecular mass first. With the unchanged example inputs, it is 180.156. Compare the additional metrics with the primary result; each has its own label and unit.
Compare and keep a useful result
The result diagram shows the inputs, method and output. A numeric chart is shown only when the calculation supports a meaningful numeric relationship.
Use Copy result or Download CSV to keep the answer. Share tool shares the page address without placing your input values in the URL. Recheck inputs and assumptions before using the result for a decision.
Molecular Weight Calculator formula
Relative formula mass = Σ(atom count × element atomic weight). Numerically, the same sum expressed as g/mol is the molar mass.
Inputs and units
| Input | Format / range | Example |
|---|---|---|
| Chemical formula | Text / numeric list | C6H12O6 |
Worked example
Using the example inputs above, the relative molecular mass is 180.156.
- Relative molecular mass
- 180.156
- Atom counts
- C:6, H:12, O:6
Results and assumptions
Uses abridged/conventional NIST periodic-table atomic weights where a standard value is available. Isotope-specific compounds require isotope-specific masses.
Sources and method references
Fix an input or unexpected result
If your answer differs from the example, choose Reset and compare every field, including selected units and options. Check percentage versus decimal entry and whether values describe the same period. Round only the final displayed answer when reproducing the formula.
If a discrepancy remains, report the calculator issue with the page address, non-sensitive example inputs, actual result, expected result and a reference for your calculation.