Quick answer: Molar mass is the mass of one mole of a substance in g/mol. Type any chemical formula (like H2O or Ca(OH)2) and this calculator gives the molar mass, element breakdown, percent composition, plus a mass-to-moles converter.
Last reviewed: September 2026
Key facts
- Molar mass = mass of one mole, in g/mol.
- Sum of atomic masses × atom counts.
- Use parentheses for groups: Ca(OH)2.
- Moles = mass ÷ molar mass.
Free molar mass calculator: formula to g/mol with element breakdown and percent composition.
How to use
- Type a chemical formula (H2O, H2SO4, Ca(OH)2).
- Read molar mass and breakdown.
- Convert mass ↔ moles.
Formula
M = Σ (atomic mass × count) n = m ÷ M
Worked examples
H2O: 2×1.008 + 15.999 = 18.015 g/mol.
NaCl: 22.99 + 35.45 = 58.44 g/mol.
Ca(OH)2: 40.078 + 2×(15.999+1.008) = 74.092 g/mol.
Frequently asked questions
Molar mass vs molecular weight?
Same number; molar mass is g/mol, molecular weight is dimensionless (amu).
How to write formulas?
Element symbols with counts: H2SO4. Use parentheses: Ca(OH)2.
What is percent composition?
Mass fraction of each element × 100.
Moles from grams?
n = mass ÷ molar mass.
Why do I need molar mass?
For stoichiometry, solution prep, and lab calculations.
Are atomic masses exact?
They are weighted averages of isotopes, updated periodically.
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