About this calculator
Brackets, square brackets and water of crystallisation all work: Ca(OH)2, K4[Fe(CN)6], CuSO4·5H2O.
How to use it
- Type the formula with correct capitals.
- Read the molar mass and composition.
The formula
Molar mass = Σ (number of atoms × atomic mass)
- Atomic mass
- standard atomic weight in g/mol
Worked example
CuSO4·5H2O
- Cu 63.546 + S 32.06 + O 9 × 15.999 + H 10 × 1.008.
- = 249.68 g/mol; copper is 25.45% by mass.
What the result means
Molar mass in g/mol has the same number as the molecular mass in u.
Assumptions
- Natural isotopic abundance.
Limitations
- Enter formulas without charges.
Frequently asked questions
Is molar mass the same as molecular weight?
Numerically yes; molar mass has units of g/mol.
Why do capitals matter?
Co is cobalt, CO is carbon monoxide.
How do I enter a hydrate?
Use a dot or star: CuSO4·5H2O or CuSO4*5H2O.
Last reviewed on 6 October 2026. Found a mistake? Tell us.