How do I enter a chemical formula?

Use element symbols with optional integer subscripts, e.g., H2O, C6H12O6, NaCl. Parentheses for groups are supported, e.g., Ca(OH)2.

Molecular weight is returned in grams per mole (g/mol), based on standard atomic weights.

What if an element is missing from the table?

You can enter a manual atomic weight for unknown or custom elements in the manual entry field and include it in the compound string as e.g. X:12.34; the tool will use that value.

Are isotopic masses supported?

This tool uses standard atomic weights (average natural isotopic composition). For isotopic-specific masses use a dedicated isotopic calculator.

Can I export results?

Yes — Copy Result and Download CSV export the molecular composition and computed molar mass.

Does it handle parentheses and nested groups?

Yes — the parser supports parentheses with integer multipliers, including nested parentheses to reasonable depth.

How accurate are the atomic weights?

Standard atomic weights are used to typical published precision (4–6 significant digits). They are suitable for most chemistry and engineering tasks but not for high-precision isotopic work.

Yes — AkCalculators provides the Atomic Weight Calculator free for educational use.

Atomic Weight Calculator — AkCalculators

Q: Is the periodic table data editable?

Yes — the sidebar includes a quick reference and you can override weights via manual entry if desired.

Atomic Weight (Molar Mass) Calculator

Enter a chemical formula (e.g., H2O, C6H12O6, or Ca(OH)2) to compute the molecular weight in grams per mole (g/mol). You can also supply manual atomic weights for custom elements.

Formula input (supports parentheses and hydrates with "." or "·") Manual element overrides (optional). Enter as Symbol:weight separated by commas, e.g. X:12.34,Y:55.0

Show element breakdown Precision

Understanding atomic weights and molar mass

Atomic weight (also called relative atomic mass) is the weighted average mass of the atoms in a naturally occurring sample of an element, measured relative to 1/12 of the mass of a carbon-12 atom. Molar mass is the mass of one mole (Avogadro’s number of entities) of a substance and has units of grams per mole (g/mol). For elements, the molar mass in g/mol numerically equals the atomic weight; for compounds, it is the sum of the atomic weights of constituent atoms in the formula.

How the calculator works

The calculator parses chemical formulas, handles parentheses with multipliers, supports hydrates written with "." or "·", and allows manual overrides of atomic weights. It looks up standard atomic weights for common elements and sums contributions to give a final molecular weight. For rational design or isotopic-specific work, use isotope-specific masses with specialized tools.

Examples and usage

Common examples: Water H2O → 2×1.008 + 16.00 ≈ 18.02 g/mol. Glucose C6H12O6 → 6×12.011 + 12×1.008 + 6×16.00 ≈ 180.16 g/mol. Calcium hydroxide Ca(OH)2 handles the (OH)2 group as two oxygens and two hydrogens bound to Ca.

Precision and standard values

Standard atomic weights are taken from widely used tables and are given to a few significant figures suitable for most laboratory calculations. For higher precision or isotopically labelled samples, consult specialized references or isotope mass tables.

Limitations

This calculator uses average standard atomic weights and is intended for educational and routine lab calculations. It does not perform isotopic separation or high-precision mass spectrometry-level calculations.

Use the input box above to try your formulas; the sidebar contains a quick reference list of common elements and weights for convenience.

Frequently Asked Questions

1. How do I enter polyatomic groups?
Use parentheses, e.g., Ca(OH)2. The number after the parenthesis multiplies the whole group.

2. Can I calculate ionic compounds?
Yes — enter the empirical formula (e.g., NaCl). The calculator sums atomic weights of formula units.

3. How are hydrates entered?
Use a dot or middle-dot: CuSO4.5H2O or CuSO4·5H2O. The parser treats the hydrate as an added group.

4. Why does my result differ slightly from other tables?
Different sources report atomic weights with varying precision or reference isotopic composition; small differences are expected at the third or fourth decimal place.

5. Can I override atomic weights?
Yes — use the manual overrides field, e.g., X:12.34 to define a custom element weight.

6. Does it support nested parentheses?
Yes — nested parentheses to reasonable depth are supported by the parser.

7. Are units shown?
Results are in grams per mole (g/mol).

8. Is the periodic table data editable?
You can override specific element weights via the manual entry box; a full editable table is not included in this UI.

9. Can I get a breakdown of contributions?
Yes — enable "Show element breakdown" to see each element count and contribution to the total molar mass.

10. Is this tool free?
Yes — AkCalculators provides this tool free for educational use.