Molar mass calculator
Enter a formula and get its molar mass, broken down by element.
Work it out
A worked example
CuSO₄·5H₂O
249.68 g/mol
- 1Copper contributes 1 × 63.546 = 63.546 g/mol.
- 2Sulfur contributes 1 × 32.067 = 32.067 g/mol.
- 3Oxygen contributes 9 in total — four in the sulfate and five in the waters — 9 × 15.999 = 143.99 g/mol.
- 4Hydrogen contributes 10 × 1.008 = 10.08 g/mol.
- 5Adding those gives 249.68 g/mol.
What this assumes
- Standard atomic weights are used, so the answer is an average over natural isotope abundances. A mass spectrometry calculation wants the monoisotopic mass instead, which is a different number.
The terms used here
- Molar mass
- The mass of one mole of a substance, in grams per mole. Numerically the same as the formula weight.
- Hydrate
- A compound crystallised with water in its lattice, written after a dot: CuSO₄·5H₂O carries five waters per formula unit.
- Standard atomic weight
- The average mass of an element's atoms weighted by how common each isotope is on Earth.
Where to next
Molarity calculator
Turn that molar mass into a concentration, or a mass to weigh out.
Empirical formula calculator
Go the other way: percentages by mass back to a formula.
The periodic table
The atomic weights this calculator adds up, with where each comes from.
Molecules A–Z
Named structures with their formula, mass and identifiers already worked out.
The other calculators
Molarity calculator
Relate concentration, volume and moles. Leave the unknown blank.
Dilution calculator (C₁V₁ = C₂V₂)
C₁V₁ = C₂V₂. Leave the unknown blank.
Percent yield calculator
Actual over theoretical, as a percentage. Leave the unknown blank.
Beer–Lambert law calculator
A = εlc. Leave the unknown blank.
pH, pOH and [H⁺] calculator
Convert between pH, pOH, [H⁺] and [OH⁻]. Leave the unknown blank.
Buffer pH calculator (Henderson–Hasselbalch)
pH = pKa + log([A⁻]/[HA]). Leave the unknown blank.
This calculator runs in your browser. Nothing you type is sent anywhere, and no account is needed. If you want to go further than arithmetic — look a structure up, see what a reaction has been recorded as giving, or follow a mechanism — the library is open too.