Molecular Weight Calculator (formula → molar mass & composition)

Q: "Do you support parentheses and hydrates?"

"Yes. Common notation (e.g., CuSO4·5H2O) and nested parentheses are supported. Note that '.' is ambiguous, so a warning appears when used."

Q: "Which atomic weights are used?"

"The selected atomic weight table (IUPAC, etc.) and version are shown in the results. Share URLs reproduce the same settings later."

Q: "Can I use it for reaction equations?"

"For reaction coefficients and equivalents, use the next tool (Stoichiometry Calculator). This tool focuses on formula mass and composition."

Q: "Is molecular weight different from molar mass?"

"In this tool they are treated as the same numeric value, with units shown as g/mol and Da."

Q: "Can I specify isotopes (e.g., 13C)?"

"Enable isotope notation in Advanced settings to parse [13]C and similar. The default uses natural isotopic abundances."

Calculate molar mass and elemental composition (mass %) from a chemical formula. Parentheses and hydrates (CuSO4·5H2O) supported. Copy or export results as CSV.

Example C6H12O6 Ambiguous notation triggers a warning (e.g., '.' usage).

Calculate molar mass from a chemical formula

Formula input

Chemical formula Supports parentheses (), brackets [], and hydrates (·/・). Ambiguous notation shows warnings.

Example chips

Tap to insert and calculate

詳細設定

Significant figures Atomic weight table

Enable isotope notation

Isotope notation Use mass numbers in brackets, e.g., [13]C.

Allow non-integer coefficients ASCII '.' handling If input looks like CuSO4.5H2O, a warning appears and the interpretation is shown.

Recent formulas

暫無歷史紀錄

Results (molar mass / molecular weight)

結果

Results appear here

Elemental composition (mass %)

Shows counts, mass contribution, and mass percent per element.

Element	Count	Atomic weight	Mass contribution	Mass %
總計			Total mass	Total %

How to use and supported notation

Enter a formula and click Calculate. The interpreted formula is always displayed so you can verify the parsing.

Parentheses and brackets

Nested ( ) and [ ] are supported. Example: Al2(SO4)3

Hydrates (additive)

· • ⋅ ・ are treated as hydrate separators. Example: CuSO4·5H2O

Coefficients

Numbers after elements or groups are treated as coefficients. Example: (SO4)3

Charge notation

Charge like SO4^2- / NH4+ is ignored for mass calculation.

注意事項

'.' can mean a decimal point or a hydrate separator, so a warning appears when it is used.
Enable isotope notation in Advanced settings.
Allow non-integer coefficients in Advanced settings (e.g., Fe0.95O).

常見問題

Do you support parentheses and hydrates?

Yes. Common notation (e.g., CuSO4·5H2O) and nested parentheses are supported. Note that '.' is ambiguous, so a warning appears when used.

Which atomic weights are used?

The selected atomic weight table (IUPAC, etc.) and version are shown in the results. Share URLs reproduce the same settings later.

Can I use it for reaction equations?

For reaction coefficients and equivalents, use the next tool (Stoichiometry Calculator). This tool focuses on formula mass and composition.

Is molecular weight different from molar mass?

In this tool they are treated as the same numeric value, with units shown as g/mol and Da.

Can I specify isotopes (e.g., 13C)?

Enable isotope notation in Advanced settings to parse [13]C and similar. The default uses natural isotopic abundances.

Next: Stoichiometry calculator

Need reaction coefficients or equivalents?

Go to stoichiometry calculator

Disclaimer & references

Disclaimer

Results are for reference. Verify with primary sources or measurements for critical use cases.

參考表

IUPAC Standard Atomic Weights (ver: 2021-11-12)