Molecular Weight Calculator

Enter a chemical formula to get its molar mass in g/mol using IUPAC standard atomic weights. The parser handles nested parentheses and brackets, hydrates such as CuSO4·5H2O and a leading coefficient. A breakdown table shows how many atoms of each element there are, their contribution to the total mass and the mass percent composition.

How to use the Molecular Weight Calculator

1. Type a formula with correctly capitalised symbols, e.g. Ca(OH)2 or K4[Fe(CN)6].
2. Use · or a full stop for hydrates, e.g. CuSO4.5H2O.
3. Read the molar mass and the per-element breakdown as you type.
4. Copy the result or download the breakdown as CSV.

Features

• Nested ( ), [ ] and { } groups
• Hydrates and leading coefficients
• Mass contribution and mass percent for each element
• Hill formula and mass of a single molecule
• Clear errors for unknown or mis-capitalised symbols

Benefits

• Get molar masses for stoichiometry and solution preparation
• Find percent composition for empirical formula problems
• Live results with no button presses

Frequently asked questions

Is molecular weight the same as molar mass?

Numerically, yes. Molecular weight is a relative mass with no units, while molar mass is the same number in grams per mole.

Which atomic weights are used?

IUPAC abridged standard atomic weights, for example H 1.008, C 12.011 and O 15.999. For elements with no stable isotopes the mass number of the most stable isotope is used and flagged.

Why is my formula rejected?

Symbols are case-sensitive and must start with a capital letter. "co" is not valid; "Co" is cobalt and "CO" is carbon monoxide. Brackets must also be closed.

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