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Formula → g/mol
Molar mass calculator
Enter a molecular formula. Parentheses, square brackets and hydrates are supported.
Molar mass = Σ (atomic mass × number of atoms)
Calculated molar mass203.295 g/mol
Mg1 atomCl2 atomsH12 atomsO6 atoms
Molar mass calculator
Molar mass calculator for formulas, groups and hydrates.
Enter a chemical formula to calculate its molar mass and atom composition. The parser supports parentheses, square brackets and hydrate-dot notation.
Mathematical formula
Sum each element's atomic contribution
M = Σ niAi
Worked problems
Follow the units through each step.
Sulfuric acid, H₂SO₄
Problem: Find the molar mass of H₂SO₄.
- Count atoms: H = 2, S = 1 and O = 4.
- Hydrogen contribution: 2 × 1.008 = 2.016 g·mol⁻¹.
- Sulfur contribution: 1 × 32.06 = 32.06 g·mol⁻¹.
- Oxygen contribution: 4 × 15.999 = 63.996 g·mol⁻¹.
- Add the contributions: 2.016 + 32.06 + 63.996.
Answer: M(H₂SO₄) = 98.072 g·mol⁻¹.
Copper(II) sulfate pentahydrate
Problem: Find the molar mass of CuSO₄·5H₂O.
- Expand the hydrate: Cu = 1, S = 1, O = 9 and H = 10.
- CuSO₄ contribution: 63.546 + 32.06 + (4 × 15.999) = 159.602 g·mol⁻¹.
- Five waters contribute 5 × [(2 × 1.008) + 15.999] = 90.075 g·mol⁻¹.
- Add anhydrous salt and water contributions.
Answer: M(CuSO₄·5H₂O) = 249.677 g·mol⁻¹.