What atomic weight values does this tool use?

The tool uses the 2021 IUPAC Table of Standard Atomic Weights. For elements with variable atomic weight (e.g. Li, B), the conventional value recommended by IUPAC for commerce and education is used.

Does it support parentheses in formulas?

Yes. Formulas like Ca(OH)2, Al2(SO4)3, and Fe2(C2O4)3 are fully supported including nested parentheses. Multiply the count inside the brackets by the subscript outside.

What is the difference between atomic mass and molar mass?

Atomic mass is the mass of a single atom in unified atomic mass units (u or Da). Molar mass is the mass of one mole of that substance in grams per mole (g/mol). They share the same numeric value but different units.

Can I calculate the mass of an element (single-atom formula)?

Yes. Enter the element symbol alone — e.g. "Fe" returns 55.845 g/mol. The tool handles both single elements and multi-element compounds.

Why does my result differ slightly from a textbook?

Textbooks sometimes round atomic weights to fewer decimal places. This tool uses the full IUPAC 2021 conventional values. Minor rounding in textbook problems is normal and does not indicate an error.

What happens if I enter an invalid formula?

The tool displays an inline error message explaining the problem. Common issues include unknown element symbols, unbalanced parentheses, or formulas starting with a lowercase letter.

Atomic Mass Calculator

Type any chemical formula (e.g. H2O, C6H12O6, Ca(OH)2) and instantly get its formula mass and molar mass using IUPAC standard atomic weights.

Chemical Formula

Supports parentheses and all 118 elements.

Formula

Use standard element symbols (H, He, Li …). Subscripts are plain numbers.

Quick Examples

Enter a chemical formula to calculate its formula mass or molar mass.

Formula Mass / Molar Mass

— g/mol (or u / Da)

Formula:

Element Breakdown

Element	Count	Atomic Wt.	Contribution	Mass %

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Summary

Type any chemical formula (e.g. H2O, C6H12O6, Ca(OH)2) and instantly get its formula mass and molar mass using IUPAC standard atomic weights.

How it works

Type a valid chemical formula into the input field (e.g. H2O, NaCl, Ca(OH)2, Al2(SO4)3).
The parser reads element symbols and their subscript counts, respecting nested parentheses.
Each element's atom count is multiplied by its IUPAC standard atomic weight.
The contributions are summed to produce the total molar mass in g/mol.
A breakdown table shows each element, its atom count, atomic weight, total contribution, and mass percent.
Click "Copy" to copy the molar mass value to your clipboard.

Use cases

Calculating molar mass of reagents before preparing lab solutions.
Verifying molecular weights during stoichiometry homework.
Checking the formula weight of ionic compounds such as salts and acids.
Finding mass percentages of each element in a compound.
Teaching or studying how atomic weights combine in a formula.
Quick reference during chemistry exams or research.

Frequently Asked Questions

Last updated: 2026-09-13 · Reviewed by Nham Vu