Molar mass calculator
From a chemical formula to every atom’s contribution.
Start with a formula
Use the element symbols exactly as they appear in the table.
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Calculated molar mass Calculated
H2O
18.015g/mol
3 atoms in the formula2 elements
The mass of one mole of this formula’s atoms.
Elemental composition
Composition of H2O
| Element | Atoms | Atomic mass (u) | Contribution (g/mol) | Mass percentage |
|---|---|---|---|---|
| HHydrogenAtomic number 1 | 2 | 1.008 | 2.016 | 11.19% |
| OOxygenAtomic number 8 | 1 | 15.999 | 15.999 | 88.81% |
| Total | 3 | — | 18.015 | 100.00% |
How the calculation works
Multiply each element’s atomic mass by its atom count, then add the contributions. Group counts apply to every atom inside the group.
Molar massΣ (atomic mass × atom count)
Values use this atlas’s atomic masses and are rounded only for display. Representative isotope masses are used where an element has no stable isotopes.