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Molecular Weight Calculator

Find the molecular weight (molar mass) of a compound from its chemical formula.

How it works Report a problem

Molecular Weight Calculator

Enter a chemical formula like H₂O, NaCl, C₆H₁₂O₆ to get the molar mass

MW = Σ(atomic weight × count)  |  units: g/mol

Use standard element symbols. Subscripts as numbers (H2O not H₂O).

Molar Mass
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in kg/mol
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in Da (u)
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1 mol = ? g
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ElementCountAtomic WtSubtotal
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Every mole calculation starts with a number: the compound's molar mass, built by adding the atomic masses of every atom in its formula. This calculator parses formulas, counts the atoms and returns the molecular weight in grams per mole.

How to use this calculator

  • Enter the chemical formula, for example H2SO4 or C6H12O6.
  • Press calculate to see the molar mass and the contribution of each element.

Parentheses are where errors breed

Formulas like Ca(OH)2 multiply everything inside the brackets by the number outside. Miscounting there silently corrupts every later step built on the mass, which is exactly why an atom-by-atom breakdown, shown by this calculator, is worth a glance before the number is used.

Frequently asked questions

How is molecular weight calculated?
Add the atomic mass of every atom in the formula: count of each element times its atomic mass, summed over all elements.
Are molecular weight and molar mass the same?
In practice, yes for everyday work: molecular weight is the relative mass, molar mass is the same value expressed in grams per mole.
What is the molar mass of water?
About 18.02 g/mol: two hydrogen atoms (about 1.008 each) plus one oxygen (about 16.00).